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This win lifts United level on points with leaders Manchester City, albeit having played two games more than their bitter rivals. As for Southampton, they are without a point in four Premier League matches and stay in 12th after this historically bad result.
Manchester United put nine goals past Southampton in a record-equalling Premier League victory. Jankewitz was sent off for the visiting side a little over a minute into his debut and United took full advantage through goals from Wan-Bissaka, Rashford, Cavani and a Bednarek own goal before half-time. Adams had a goal ruled out and United then added to their tally, with Martial netting twice either side of McTominay's drive and Fernandes converting a penalty that saw Bednarek red carded. James rounded off the scoring in added time.
90' + 4' FULL-TIME: MANCHESTER UNITED 9-0 SOUTHAMPTON
90' + 2' Manchester United last won a match by an eight-goal margin in March 1995 v Ipswich Town.
90' + 1' Three minutes have been added on at the end of the game.
90' Manchester United have scored seven goals in a match for the first time since winning 8-2 against Arsenal in August 2011.
84' PENALTY TO MAN UNITED! Bednarek, who has already scored an own goal today, appears to clip Martial in the box and Mike Dean points to the spot. It will go to a VAR check to see if the Southampton defender definitely made contact.
83' United are not letting the tempo of the game drop. They are continuing to push for more goals, perhaps knowing that goal difference may well play a part in the title race this term.
82' SAVE! The introduction of defender Tchaptchet means a slight change in shape for Southampton. United keep coming forward, though, with Greenwood's shot being kept out by McCarthy at his near post.
80' Fernandes looks to pick out the top-right corner but his range is a little off and the ball ends in the stands.
79' Only Eric Cantona and Dimitri Payet (both 33 games) have assisted 15 Premier League goals in fewer appearances than Bruno Fernandes, with this his 36th appearance in the competition for Manchester United.
77' Southampton have completely crumbled over the last 10 minutes. James is the latest to race through on goal but, with the angle against him, he is forced to cross rather than shoot and cannot pick out Martial.
75' IT SHOULD BE SEVEN! Martial is played clean through on goal. McCarthy is caught in two minds and the United striker looks to lift the ball over the Southampton keeper. It looks destined to end in the back of the net, only to spin wide of the unguarded net.
73' SITTER! Redmond lays one on a plate for Adams. Seven yards out, the striker scuffs a shot over the crossbar with plenty of the target to aim for.
68' Ings takes no risks as he chests a whipped cross behind for another United corner. The set-piece is cleared as far as Fred, who sees his shot from 20 yards closed down.
66' Greenwood and Martial exchange passes in the opposition box but Southampton stand their ground at the back. Wan-Bissaka appears to have injured himself when tackling Ings a few minutes ago - that is one to keep an eye on.
64' The game is just petering out a little now. Hasenhuttl will be pleased with the response from his side in this second half, though ultimately it is too little too late.
63' Southampton deal with a few crosses into the box from United. James is played in behind by Fernandes but cannot find a team-mate in the middle.
62' Even in a one-sided match like this, VAR will still be a big talking point after the game. United were denied what they felt was a clear penalty in the first half; Southampton have been denied a consolation goal through a contentious offside call.
59' Twenty-four per cent of the Premier League goals Southampton have conceded this season have been against Manchester United (7/29).
57' SAVE! Fernandes seems desperate to get his name on the scoresheet today. He has a go from 25 yards and McCarthy makes another good stop down low. The ball bounced right in front of the keeper, making it all the more difficult to get behind.
55' GOAL DISALLOWED! Adams was marginally offside when latching onto Ward-Prowse's smart free-kick and the goal is ruled out by VAR. Cruel on Southampton, that.
54' GOOOOAAAALLL!!! MAN UNITED 4-1 SOUTHAMPTON!! Well there's one back for the visitors! Ward-Prowse catches out United with a free-kick down the line for Adams. The striker's first shot is blocked but persistence pays off as he fires a second shot through the legs of Maguire and away from De Gea. However, VAR is checking for a possible offside...
52' Martial plays a great one-two with Fernandes and is in on goal. Van de Beek blocks his view, though, and when he does get the delayed shot away it is blocked four yards out.
51' Wan-Bissaka works a yard of space and crosses towards Martial in the six yard box. Southampton clear the ball at the second attempt.
50' The second half has got off to a slow start. Southampton are desperately trying to keep hold of the ball but are not really able to ask any questions of their opponents.
48' United have Everton at the weekend, and some European games on the horizon, so it is little surprise that Solskjaer has opted to rest key men Cavani and Shaw.
46' RESTART! United get us back under way at Old Trafford. Will Solskjaer's men add to their goals tally in the second half?
Southampton can perhaps consider themselves fortunate not to be five goals down at the break, as United were awarded a penalty late in the half that was overturned by VAR. The visitors will surely focus on damage limitation in the second period, while Solskjaer will be after more goals from his side, who have four goals from six shots on target.
United lead 4-0 at the interval in one of the most one-sided first halves of Premier League football you are likely to see. Jankewitz was sent off a little over a minute into his senior debut and Southampton collapsed, conceding to goals from Wan-Bissaka, Rashford, Cavani and Bednarek, who put into his own net.
45' + 2' HALF-TIME: MANCHESTER UNITED 4-0 SOUTHAMPTON
45' + 1' Fernandes drives a low free-kick into the Southampton wall. United are annoyed not to have been given a penalty - the contact from Ramsay on Cavani did appear to be on the line, meaning a penalty should have been awarded.
43' PENALTY OVERTURNED! The VAR officials deem that the contact was made just outside the area, so it will be just a free-kick for United and not a penalty.
42' PENALTY TO MAN UNITED! It could get worse for Southampton. Ramsay fouls Cavani right on the edge of the box and referee Mike Dean points to the spot. VAR will double-check to see where the contact was made...
41' Southampton are the first team to have a player sent off and score an own goal in a Premier League game against Manchester United at Old Trafford since Sunderland in October 2009.
38' Fernandes knocks the ball into Wan-Bissaka's path and the full-back crosses to Cavani. The striker's shot is blocked by Ramsay in front of goal as Southampton survive another scare.
36' OVER! United's players are queuing up to strike the ball. McTominay is the latest player to take on a shot from range, miscuing his effort into the stands from 20 yards.
33' Fernandes' teasing cross from the right is brilliantly defended by the head of Stephens. The corner is cleared as far as Shaw, whose powerful drive is dealt with by McCarthy.
32' FERNANDES DENIED! Rashford cuts inside and lays the ball off to Fernandes 20 yards from goal. The Portuguese has time to get a shot off and forces a good low save out of McCarthy, with the ball bouncing just in front of the Southampton goalkeeper.
31' Southampton have looked good since going two goals behind. The visitors are knocking the ball around and are trying to get in behind their opponents. They have a huge mountain to climb, though.
29' De Gea also stands his ground from the resulting corner by punching the ball clear.
28' GREAT SAVE! Free-kick specialist Ward-Prowse is denied by a superb De Gea save. The Southampton skipper gets the free-kick around the wall but De Gea is well positioned to palm the ball over the crossbar.
26' That goal for Rashford ends a run of six Premier League games without finding the back of the net.
24' Manchester United right-back Aaron Wan-Bissaka has two Premier League goals this season, having never scored in any of his previous three seasons in the competition.
22' Shaw has another chance to send in a delivery from the left, this time from a free-kick. It is once again crossed into a dangerous zone, but Lindelof - who was offside anyway - is unable to convert.
20' Ward-Prowse does well to track back and intercept the ball before Fernandes can pull the trigger. That came after a Southampton corner at the other end, which ended with a free-kick being awarded for a foul on De Gea.
18' GOOD ATTEMPT! This is a reminder that United cannot afford to throw everyone forward. Adams holds the ball up, tees up Ward-Prowse and the midfielder's long-ranger is not far wide from goal at all.
17' SHOT! Rashford's weak attempt from 20 yards takes a slight deflection but is a simple one for McCarthy to deal with down the middle.
16' United are working the ball from side to side to stretch their 10-man opponents. McTominay sends a delightful ball into the middle, but Bednarek gets a vital touch to the ball before Cavani can turn it in.
14' Southampton's players have been told to stop pressing United high up the pitch. This is going to be an exercise in attack-against-defence for 90 minutes, you feel.
12' Southampton are sitting deep, as you would expect with 10 men, and are doing well to keep United's attacking players quiet. Rashford wasted the best of their openings shortly after the sending off.
10' The more you see that Jankewitz challenge on McTominay the worse it looks. Even Hasenhuttl was a little stunned on the sidelines.
9' Fred looks to curl a right-footed shot into the top corner but gets far too much on it and sends the ball into the stands.
8' Armstrong has shifted into midfield and Ings has moved into a wide position. Southampton's task was always going to be difficult today - it has now become a lot harder following that early dismissal.
6' Alexandre Jankewitz is one of only four players to be sent off in the opening two minutes of a Premier League game. Tim Flowers (Blackburn Rovers v Leeds United, Feb 95), Ben Thatcher (Wimbledon v West Ham, Dec 97) and Gareth McAuley (West Brom v Man City, Mar 15) are the others on that list.
4' Rashford is played in behind. He has the option of opening up his body and going for goal himself, but he unselfishly pulls the ball back for Fernandes and Southampton cut it out.
3' That really was a shocking challenge from Jankewitz, just 82 seconds into his senior bow. McTominay is back on the field after receiving some treatment.
1' KICK-OFF! A depleted Southampton side get us up and running at Old Trafford, where they are aiming to pull off a surprise result.
Both sets of players are now out on the field at Old Trafford and kick-off is just a few moments away. Southampton can climb into the top half with a victory today, while three points for United would take them level with Manchester City at the summit, albeit having played two games more.
Manchester United are unbeaten in their last nine Premier League meetings with Southampton (W4 D5), though they are looking to complete their first league double over the Saints since their title-winning campaign of 2012-13. The reverse fixture in November finished 3-2 in United's favour.
Hasenhuttl has made four changes to Southampton's starting line-up following Saturday's 1-0 home loss to Aston Villa. Theo Walcott, Ibrahim Diallo and Oriol Romeu miss out through injury, while Redmond is named among the subs. That means a first senior start for Jankewitz in midfield and a second Premier League start for fellow youngster Ramsay. Djenepo and Adams are also recalled.
United show one change from their stalemate at Arsenal three days ago, with Greenwood being brought into the side in place of the benched Pogba - the first league game the France international has not started since Boxing Day. McTominay was considered a fitness doubt for this contest, but he has recovered from a stomach issue to join Fred in the engine room.
Subs: Daniel N'Lundulu, Will Ferry, Harry Lewis, Ryan Finnigan, Nathan Redmond, Kgagelo Chauke, Fraser Forster, Allan Tchaptchet.
SOUTHAMPTON XI (4-4-2): Alex McCarthy; Kayne Ramsay, Jan Bednarek, Jack Stephens, Ryan Bertrand; Stuart Armstrong, James Ward-Prowse (c), Alexandre Jankewitz, Moussa Djenepo; Che Adams, Danny Ings.
Subs: Alex Telles, Brandon Williams, Daniel James, Nemanja Matic, Donny van de Beek, Eric Bailly, Anthony Martial, Dean Henderson, Paul Pogba.
MAN UTD XI (4-2-3-1): David de Gea; Aaron Wan-Bissaka, Victor Lindelof, Harry Maguire (c), Luke Shaw; Scott McTominay, Fred; Marcus Rashford, Bruno Fernandes, Mason Greenwood, Edinson Cavani.
Southampton head into this match on the back of three successive league defeats, including a 1-0 home reverse at the hands of Aston Villa last time out. Ralph Hasenhuttl's men have slipped down the division, but they can move into the top half with victory today.
United recently led the way at the top of the division, but one win in their last four top-flight matches - most recently playing out a goalless draw away at Arsenal - has seen them slip three points behind leaders Manchester City, who have a game in hand.
Hello and welcome to our live text coverage of the Premier League meeting between Manchester United and Southampton at Old Trafford.
