Manchester United FC recovered from an early setback as two second-half headers from Wayne Rooney helped them to a first ever win at San Siro, though Clarence Seedorf's late effort leaves AC Milan with every hope in this UEFA Champions League first knockout round tie.
That United held on at all in the second half was an achievement in itself after Ronaldinho had given the hosts a third-minute lead. The Serie A side squandered chances to extend their advantage and Paul Scholes' fortuitous equaliser gave the visitors a foothold before Roooney's two headers put Sir Alex Ferguson's men in control. Substitute Seedorf's late strike made for an exciting climax, with Michael Carrick sent off for a second bookable offence, but United held on.
Leonardo had said his side needed a "flawless" performance and they got off to the perfect start when Ronaldinho struck in their very first attack. Playing against his former side, David Beckham was involved, swinging a free-kick into the box, but the chance arose more as a result of Patrice Evra's miscued clearance than any set-piece artistry. The ball fell to Ronaldinho on the edge of the area and the Brazilian fired in first time off Carrick's legs, before embarking on a festive samba.
The goal set the tone for a first half dominated by the hosts. Emboldened by their start, Pato created another opening for Ronaldinho though this time, without a deflection to contend with, Edwin van der Sar was equal to it. United were under pressure, and fortunate not to go two down when Thiago Silva threaded a pass into the area for Luca Antonini, who pulled his shot wide from 12 metres.
The visitors mustered a hopeful attempt from Scholes, and Rooney went closer with an angled drive but the Premier League champions were uncharacteristically ceding possession. Rio Ferdinand was a case in point, heading the ball into the path of Pato, whose shot was blocked by Evra. Another mix-up enabled Massimo Ambrosini to pick out Klaas Jan Huntelaar, who drove just wide.
For all the hosts' dominance, they were pegged back by United's first real attack on 36 minutes. Darren Fletcher found space on the right and his low centre was met by Scholes' standing foot, the ball going in off the far post. Milan reacted well, Ronaldinho testing Van der Sar either side of half-time and Pato powering Giuseppe Favalli's header over.
Rooney was beginning to show glimpses of his explosive power, forcing Dida into a save just after the hour. Yet when his first goal came on 66 minutes it was out of the blue as he headed Antonio Valencia's cross back across the goalkeeper just moments after the Ecuadorean's introduction. Milan were rocked, forced to defend ever deeper and eight minutes later Rooney inflicted further damage, beating the offside trap to glance in Fletcher's cross.
Home hopes rose five minutes from time when Ronaldinho created space for a left-wing centre which substitute Seedorf flicked in to make for a rousing finale. Filippo Inzaghi blazed over, Thiago Silva headed high from a metre out but the hosts could not find the equaliser and will head to Old Trafford on 10 March needing a win.