The ex-Bianconeri boss was shocked by the gulf in quality between the two teams in a heavyweight Champions League clash at the Allianz Stadium
Barcelona could have scored eight against a Juventus side lacking speed across the pitch, according to Fabio Capello.
Barca stormed to the top of Group G by picking up an impressive 2-0 victory in Turin on Wednesday night.
The battle between two European giants had been highly anticipated since the draw for this season's group stages at the start of the month, with supporters and experts excited by the prospect of Lionel Messi and Cristiano Ronaldo renewing their rivalry.
However, Juve had to make do without Ronaldo after he was tested for Covid-19 again before the contest, having first been diagnosed with the virus while away on international duty with Portugal.
The Italian giants lacked inspiration in the final third in the absence of a talismanic figure, while Messi and Co produced their best performance of the new season to date to bounce back from a 3-1 defeat to Real Madrid at the weekend.
Ousmane Dembele's deflected strike from long-range gave Barca a deserved 14th-minute lead, but he also squandered a glorious chance to double the visitors' lead before the break.
Messi and Griezmann were also guilty of wasteful finishing, while at the other end, Alvaro Morata found the back of the net on three occasions only to be denied by the offside flag.
Barca finally rounded off a morale-boosting win in stoppage time as Messi coolly converted from the penalty spot, with Capello left surprised with the gulf in quality between the two sides.
"Juventus suffered a lot against a Barcelona in crisis. I was struck by the difference between a team under construction that also lost the Clasico and one at the top in Italy," the ex-Juve boss told Sky Sports post-match.
"I was shocked by the difference in intensity and play. Barcelona really impressed me, they could have scored eight goals instead of two.
"I saw an aggressive team and a lot of dynamism. Messi also contributed a lot."
Capello added on Juve's failure to create openings going forward and Barca's superiority in terms of energy levels: "[Federico] Chiesa was often free [in midfield] but all the bets were always concentrated on [Paulo] Dybala and his side.
"It was therefore not possible to open the game and therefore Barcelona had a chance to recover the ball quickly. There was another speed and this makes me doubt what we have in Italy.
"It was all of Juve that lacked speed, they were always pressed and anticipated."