A penalty deep into second-half stoppage time from Luis Suarez gave Atletico Madrid a dramatic 2-1 Champions League win over Milan at San Siro.
Antoine Griezmann scored his first goal since his return to the club to level the scores in the 84th minute after Rafael Leao had deservedly put the hosts in front.
Franck Kessie received a second yellow card after only 30 minutes, but Stefano Pioli's men remained impressively resolute until Griezmann's impact off the bench.
Suarez then converted from the spot in style in the seventh minute of added time after Pierre Kalulu was penalised for handball, the decision upheld after a VAR check.
In the opening 20 minutes, Milan looked faster, stronger and more dangerous than Atleti. Jan Oblak saved superbly to deny Ante Rebic but he could do nothing when Leao controlled and fired low on the turn through a crowded box and into the bottom-left corner.
That high intensity was arguably the undoing for Kessie. Having been booked 15 minutes in for a foul on Marcos Llorente, he stood on the Atleti man's foot as he harried in midfield, earning a second yellow card after only half an hour.
Diego Simeone threw on Joao Felix, who set up Suarez for Atleti's best first-half chance in injury time, the striker hooking a volley just wide of the right-hand post.
Suarez glanced a Felix cross just wide but, with chances scarce, Simeone at last turned to Griezmann for the final third of the match, and he duly delivered for his coach with a stylish volley past Mike Maignan from Renan Lodi's header.
As Atleti pushed for a winner, Kalulu knocked the ball away from Thomas Lemar's path with his arm as he tried to block the route to goal, allowing Suarez to send an impudent spot-kick down the middle.
What does it mean? Atleti consolidate second in Group B
Atletico are second in Group B, with four points from their first two games, putting them two behind leaders Liverpool.
The Rossoneri are now in need of positive results after consecutive defeats to start their campaign.
Simeone must have been ruefully impressed with Milan's defensive display for the majority of the game, with Fikayo Tomori at the heart of it.
The former Chelsea defender made a game-high nine clearances and four blocks to help the Rossoneri restrict Atleti to hopeful efforts in attack before their late flourish.
Kessie's second yellow was perhaps a little harsh but it came seconds after he had barged into another blue shirt in a moment of over-zealous pressing in midfield.
An exceptionally organised performance from Milan kept Atletico at arm's length for a long time, but it proved in vain.
On matchday three, Milan head to Porto while Atletico Madrid host Liverpool. Next up for the Rossoneri is a league trip to Atalanta on Sunday, while Atleti host Barcelona in LaLiga on Saturday.