90' + 1' We're into the first of three added minutes and - in worrying news for the hosts - McTominay has been forced off clutching his groin. Cavani meanwhile pulls an effort wide down the far end.
90' If anything sums up the Whites' evening, it is a lovely square ball from Raphinha now that Bamford steps over entirely and Harrison promptly curls wide. Leeds surely won't be parting with Marcelo Bielsa after this though.
89' It is hard to be critical of Leeds - this uncompromising approach wins them as many as they lose, and it's often a delight - but their defence has been particularly shoddy across the last 20 minutes or so, even discounting the four first-half goals.
88' The hosts have had 25 shots by the way, while Leeds have had 16. This has been a wild match.
87' Telles is the latest man to pop an effort in, which Meslier pushes away for a corner. The keeper is on hand to punch away Maguire's header a moment later - and then has to deal with a Fred effort after some appalling defensive play. Martial heads the final corner over.
85' Cavani! The Uruguayan leads a Red Devils break and sees Meslier parry his effort back out. James taps a follow-up towards goal and the keeper claims this one cleanly.
83' Eight goals. Nobody has been shortchanged on that front. Are there more to come?
81' A botched Red Devils clearance allows Harrison to poke an effort though, which the hosts deflect for a corner. Wan-Bissaka blocks that for another set-piece and Ayling nudges the subsequent effort over the crossbar.
79' This really has been the perfect storm for Leeds though, hasn't it? Manchester United have not bunkered down, they have opted to - for large parts - meet them at their own game. It has brought up their shortcomings on arguably the biggest stage of their season.
77' Consecutive Leeds corners and a waved-off penalty shout are the latest opportunities to present themselves in this match. There's been no shortage of entertainment.
75' Leeds United have had 59 per cent of possession in this match. They trail by four goals. The Premier League? Bielsaball? Both have fed into this manic game.
69' Penalty to Manchester United! Martial is brought down following a neat run by Rashford, and Struijk is the guilty party. Fernandes will take.
68' This has been a quieter half, both sides perhaps drained by both early exertions and the inability to find a sixth goal in this match. Now the hosts have it, they've got a spring in their step. Leeds are looking more withdrawn.
67' This has been a quieter half, both sides perhaps drained by both early exertions and the inability to find a sixth goal in this match. Now the hosts have it, they've got a spring in their step. Leeds are looking more withdrawn.
64' Raphinha! A volley from the winger is tipped away from the left corner by De Gea, though it looked destined for the side netting regardless.
62' Bamford looks to take an accidental finger in the eye from Maguire during a high challenge. The latter puts the ball out for a throw-in so he can be checked and Leeds restart by putting their throw-in straight back to De Gea.
58' Manchester United's power on the counter so far is just looking more potent than that of their visitors. Fernandes wins another corner, Meslier punches it away and Leeds survive this latest attempt.
56' Bamford drills an effort in following a Harrison cut-back, and sees his deflected effort countered by James once more. He draws the foul in midfield and wins the free-kick.
54' Manchester United's power on the counter so far is just looking more potent than that of their visitors. Fernandes wins another corner, Meslier punches it away and Leeds survive this latest attempt.
54' End-to-end corners now, as Harrison wins a strong effort and promptly sees the Red Devils counter. Rashford lays on Fernandes and a deflection wins him a set-piece that sails past the unmarked Portuguese.
50' Raphinha! De Gea makes a great stop to deny the winger, who comes close to wrestling a cross in at the left side. The deflection still requires the post and Wan-Bissaka to put it out for good measure.
49' These changes at the break from Leeds could add a shade of extra nuance to their play. But they will undoubtedly refuse to sit back here.
47' Martial! That should have been a fifth goal for the hosts. Dallas is sloppy inside his own half and allows Fernandes to pick his pocket. He plays the striker in, who then scuffs a sitter wide of the right post.
46' We're back underway for the second half at Old Trafford. What have Leeds got up their sleeve for this second act - and will it be as plain sailing to deal with as Manchester United hope?
Ole Gunnar Solskjaer looked honestly a little shellshocked as he walked off there - and his side are ahead! That's just what a crackpot match this has been. The Red Devils are on for three points - but there's a long way to go yet.
We expected fireworks but perhaps not quite like that. Marcelo Bielsa's uncompromising tactical vision has come unstuck on occasion in the top-flight, but arguably never as much as today - and yet, you wouldn't put it past his side to pull something out of the hat.
A Scott McTominay double inside the first three minutes? Just the tip of the iceberg in this absolutely barmy game that has seen Manchester United have less ball than Leeds United - and remarkably lead by three goals. Efforts for Bruno Fernandes, Victor Lindelof and Liam Cooper have added to a riotously entertaining Premier League match. Half-time at Old Trafford, it is Manchester United 4-1 Leeds United.
45' + 3' HALF-TIME: MANCHESTER UNITED 4-1 LEEDS UNITED
45' + 2' Some sloppy work from Lindelof around the back allows Bamford to almost pounce, with a goal-kick given after the ball flies out of play.
45' + 1' We're into the first of two added minutes in this opening half. There's not been many better games for neutrals this season in the Premier League, and that really is saying something.
45' Rashford! The striker trades the ball between his feet from the set-piece and fires low from outside the box, with Meslier getting down low to make the stop.
44' Corners at both ends in the space of 90 seconds now, with Leeds flagged offside at their own set-piece and Rashford earning the Red Devils their own through a neat run.
41' Martial gets flagged for offside at one end and Raphinha pumps a promising cross in at the other, with a return delivery earning Leeds a corner. The visitors are refusing to lie down.
39' Marcelo Bielsa, a man who is wonderfully uncompromising in his vision. It hasn't worked out for him today; the risk has outweighed the reward, and Ole Gunanr Solskjaer has the players to pick out those defensive soft spots. There's surely more goals in this.
36' No-one will ever accuse Leeds United of not going all in. Newly promoted teams often hedge their bets in their first season. Marcelo Bielsa rips the kitchen sink out and hurls it as often as he can.
34' Raphinha! From the far side of the box, he drills the delivery from the corner in towards the right post. De Gea palms it into an offside visitor and the flag hands Manchester United the free-kick.
33' James now deflects an attempted Rodrigo cross, as Leeds continue to craft attacking options every time they get near the final third.
31' Dan James' inclusion raised eyebrows pre-match - he has been linked with finally completing a move to Leeds in the new year - but he's proved inspired so far. The visitors repel the corner with steadfast gumption.
30' Now the hosts have a corner, Ayling muscling the ball away from Martial. Rashford is having words with the referee, protesting a non-foul from Dallas that went uncalled.
29' Raphinha whips in Leeds' latest corner and the flag goes up for offside in the box. The visitors likely need the next goal here if they hope to salvage a result.
27' That being said, it has also definitely been the perfect storm of their tactical flaws so far. Harrison wins a corner and though the delivery goes nowhere, Dallas then wins a ball into the box to briefly threaten before Wan-Bissaka clears.
25' Bamford! Again, the striker goes close, nudging a free header over the crossbar after beating out Wan-Bissaka. This is far from the worst game of Marcelo Bielsa's tenure, even if the scoreline suggests it.
24' Ole Gunnar Solskjaer actually has a small smile playing around his lips. And why not? It will take some capitulation to lose from here. But Leeds are nothing if not persistent...
22' Leeds have had more ball here - of course they have! 56 per cent of it so far, as a matter of fact. The pitfalls of these Marcelo Bielsa sides, who shift form so fast up the pitch, is that a counter can tear them apart.
21' Patrick Bamford had an effort chalked off by VAR against Crystal Palace earlier this season, with the Eagles promptly scoring the very next play. There's a touch of deja vu here.
19' Bamford! Oh, the flag is up! Frustrating for the striker, who curls a deflected Rodrigo strike past De Gea at the right post, only for the linesman to have correctly flagged him in an offside position beforehand.
18' Maguire is forced into conceding a corner under pressure from Raphinha but the delivery is subsequently poor. James counters at a blistering pace and Dallas is the last defender who manages to cut him off near Leeds' penalty area.
16' Alioski comes crashing in on Rashford and concedes the foul, though the North Macedonia international escapes a yellow card. Fernandes pumps the free-kick in and Leeds repel the delivery.
14' Cooper has to execute a swift defensive block to deny a pass teased in towards Rashford. The visitors look to have fully clicked into gear now, even as they attempt to repel the hosts' high press.
13' If there were 70,000 people in Old Trafford right now, it would be bouncing. This has been a brilliant start from the hosts, bright and inventive. It's a world away from that tepid Manchester derby last week.
11' Meslier makes a clean take from the set-piece and Leeds all pile forward again. The Whites have outrun every one of their opponents in the Premier League this season.
10' Rashford! McTominay is the man rolling forward again, playing the England man in on the right. His shot is deflected, but the hosts win a corner in short order to keep up the pressure.
9' We knew this would be an entertaining match - or at the very least had high hopes it would be - but this has been madcap. Two goals inside three minutes, a raft of chances since. Madcap stuff.
8' Bamford! You wouldn't believe Leeds have conceded two already, they've been utterly single-minded since. Their attacker nudges a looping header in, then drills a throughball wide a moment later.
6' Marcelo Bielsa was crouched on his bucket, blowing on his steaming Bovril impassively after that first goal, but he is well up on his feet now. The Red Devils have flown out of the gates against his side.
4' It's almost 2-1! Raphinha gets perilously close to a square ball inside the hosts' box, one which Shaw was in no rush to clear before twigging the danger. What a frantic start!
1' We are underway in this Premier League clash between Manchester United and Leeds United!
Sir Alex Ferguson is sat, alone, in the stands on this dark, chilly evening. Of course the Scotsman was not going to miss this one.
There may be no fans at Old Trafford as the two teams emerge but surely that won't dampen the spirits here. This is a generation in the making.
That being said, a win here and Ole Gunnar Solskjaer takes his side third. So much has been made of this being a club in crisis. Three points here suggests otherwise.
Some may say this tie means nothing to Manchester United fans these days. They need their heads examining. Defeat here for the Red Devils is thoroughly unacceptable.
It doesn't come much bigger than this, does it? In years gone, whole careers at these clubs were staked on how their fared against these rivals. Who writes their name into history today?
Subs: Ian Poveda, Tyler Roberts, Kiko Casilla, Helder Costa, Pablo Hernandez, Pascal Struijk, Leif Davis, Jamie Shackleton, Oliver Casey.
LEEDS UNITED (4-1-4-1): Illan Meslier; Stuart Dallas, Luke Ayling, Liam Cooper, Ezgjan Alioski; Kalvin Phillips; Raphinha, Rodrigo, Mateusz Klich, Jack Harrison; Patrick Bamford.
Subs: Eric Bailly, Paul Pogba, Edinson Cavani, Mason Greenwood, Juan Mata, Dean Henderson, Alex Telles, Nemanja Matic, Donny van de Beek.
MANCHESTER UNITED (4-2-3-1): David de Gea; Aaron Wan-Bissaka, Victor Lindelof, Harry Maguire, Luke Shaw; Scott McTominay, Fred; Daniel James, Bruno Fernandes, Marcus Rashford; Anthony Martial.
Perhaps unsurprisingly, Leeds make no changes to the side that ran riot against Newcastle United in midweek. Will Patrick Bamford be on fire up front today?
It's five changes from the Red Devils - but the eye-catching new arrival has to be Daniel James, who saw an 11th-hour move to today's opponents collapse before signing at Old Trafford.
As for Marcelo Bielsa? This year's Best FIFA Men's Coach bronze medalist stunned Alex Ferguson in 2012 here, when Athletic Bilbao outgunned United. Now, he lives and breathes Leeds.
Neither coach is under any illusions as to the weighty legacy of this game. Ole Gunnar Solskjaer played in a fair few encounters - including their last Premier League match, in February 2004.
In a perverse way, absence has made the heart grow fonder. Leeds' top-flight exile has robbed their fans of days like these. Now, they finally reunite with the opposition they just love to hate.
It's almost one hundred years since these two first met - a goalless draw in the old Division Two in 1923. But this will be far from a tepid encounter. This is the modern-day War of the Roses.
To quote the Stone Roses, this is the one. Football's biggest inter-city rivalry on British shores has been absent for a generation - and today, it finally returns at the top of the festive tree.
Hello and welcome to live coverage of the 2020-21 Premier League season as Manchester United finally reignite their rivalry with Leeds United after a decade apart at Old Trafford.