Atletico Madrid striker Diego Costa headed home late on to seal a 1-0 win over AC Milan on Wednesday and give a huge boost to the Spaniards' hopes of qualifying for the quarter-finals of the Champions League.
Milan had kept Diego Simeone's side on a tight leash throughout a thrilling encounter at the San Siro, but after hitting the woodwork three times in the first-half the hosts were stunned in the 83rd minute when Costa rose to head inside Christian Abbiati's near post following a corner.
Atletico, currently joint top of the Spanish top flight, will now fancy their chances of qualifying for the last eight of the competition for the first time since 1997 when the sides meet at the Vicente Calderon in a fortnight.
The visitors started crisply, stringing passes together with apparent ease and Costa holding off challenges to give Milan an early reminder of their current form.
However Atletico failed to build on that momentum and, after weathering the early storm, Clarence Seedorf's side found their feet to come agonisingly close three times in an enthralling opening half.
Simeone admitted: "After a strong start we began suffering down the right and we weren't sharp enough coming out.
"Milan came close, especially when (Thibaut) Courtois made a great save from (Andrea) Poli. We were a little slow and predictable so for the second half I boosted the midfield and that gave us the boost we needed.
"We didn't have so many scoring chances but in football the most important thing is to score, and that's what we did in the end."
Former Milan great Seedorf, in his first Champions League game as coach, applauded his side's efforts and said the tie is not over yet.
"On the whole the lads showed a lot of spirit and determination and I also saw some great individual performances," said the Dutchman.
"At the end we were tired and we perhaps paid for our efforts. It's a positive result for them but the tie is not over. I know the Vicente Calderon (stadium) well (Seedorf played for city rivals Real Madrid) but the stadium also knows me."
Milan sniffed the opener when Adel Taarabt's ball was put through for Kaka only for the Brazilian to send a curling left-footed strike off Courtois's crossbar.
Minutes later Taarabt's cross was met by Andrea Poli but Courtois performed heroics to palm the winger's precision header off the post.
Tempers flared when Emiliano Insua put in a crunching tackle on Mattia De Sciglio and, after both sets of players clashed, the Argentine was shown a yellow card.
De Sciglio tried to play on, but soon hobbled off to be replaced by Ignazio Abate.
- Dangerous on the break -
Atletico had few clear chances in the opening period, while Milan proved dangerous on the counter, just as Simeone had predicted, and they came close again on the half-hour when Balotelli's backheel found Kaka, whose latest effort skimmed the bar on its way over.
Atletico started strongly after the interval and on 52 minutes Costa was allowed space at the back post to attempt a bicycle kick when a cross was whipped in at the back post, but his effort was off target.
Kaka then sidestepped a challenge on the edge of the area but sent a tame shot wide.
Balotelli was coming in for some punishment and, before being replaced by Giampaolo Pazzini, he had a number of free-kick attempts.
One, on 65 minutes, was deflected out for a corner, from which Michael Essien sent a glancing header wide of Courtois's upright.
Atletico had the momentum in the closing stages and, on 75 minutes, Costa did well to hold off his marker and set up Raul Garcia, whose drive from 20 metres was blocked down low by Abbiati.
Seedorf replaced Balotelli with Pazzini on 77 minutes but by then a tiring Milan had little left to offer.
The visitors pressed and, after a first-time Garcia effort had just missed the target, they made the difference from a corner, which Abate inadvertently headed towards the back post where Costa met it with a powerful header of his own for his fifth goal of the campaign.