Eurosport - Mon, 08 Mar 21:48:00 2010
Rooney gave United the lead in just the 13th minute with a sublime glancing header, and the England forward netted his 30th goal of the season with a deft finish seconds after half-time to stun the visitors.
David Beckham was confined to the Milan bench at the outset and the former United midfielder had to wait until his side were 3-0 down before he was introduced, Ji-Sung Park having slammed a fierce third beyond Christian Abbiati just before the hour-mark.
Darren Fletcher capped an imperious display from the English champions with a fourth goal in the 88th minute as Milan and Beckham were left utterly shell-shocked at the final whistle.
Rooney almost gave the hosts the lead in the fourth minute as he swivelled on the edge of the Milan box to latch on to Antonio Valencia's cut-back, but he dragged his snapshot narrowly wide of Abbiati's near post.
Milan were hardly subdued in the early stages: Andrea Pirlo whipped over a devilish delivery in the eighth minute which Nani inadvertently flicked over to Ronaldinho, but the Brazilian's header drifted narrowly wide with Edwin van der Sar left flat-footed.
Two minutes later Klaas-Jan Huntelaar, who flanked Marco Borriello along with Ronaldinho, stole in at the back post beyond Patrice Evra to receive Thiago Silva's raking diagonal pass from the back, but his first touch was sloppy as the ball evaded him.
Gary Neville was preferred to Rafael at right-back for United, and Sir Alex Ferguson's decision was vindicated as the skipper picked out Rooney with a pinpoint cross from the right as United stamped their authority on the match in the 13th minute.
Rooney's exquisitely-timed run caught Daniele Bonera napping as the forward climbed above his marker to glance a deft finish beyond a helpless Abbiati and score his third headed goal in the tie.
Milan looked devoid of ideas in attack as they sought to redress the balance and, as Ronaldinho and Huntelaar were dragged out wide to gain possession, Borriello was left increasingly isolated and stifled for space.
Veteran midfielder Clarence Seedorf was introduced at half-time as the Rossoneri looked to inject some impetus into their midfield, but it was United who began the half in sparkling fashion.
Nani surged down the left wing at blistering pace before the Portugese's precise cut-back was dabbed past the onrushing Abbiati by Rooney with the utmost swagger and composure.
Milan were left horribly exposed as their three-pronged attack offered about as much defensively as they did in forward areas, and United capitalised in the 59th minute to comprehensively kill off the tie.
A procession of substitutions ensued, and the first to make his entrance was Beckham - to a standing ovation from the Old Trafford crowd.
Rooney was withdrawn to a rapturous reception as the forward was denied a potential second hat-trick, and Scholes and Neville departed swiftly afterwards.
The second half petered out after the flurry of replacements were rattled through, but a moment of brilliance from Beckham almost reignited the contest: his rasping volley from the edge of the United box was tipped away by Van der Sar.
The evening was capped off by Fletcher in the 88th minute as the midfielder capitalised on more shoddy defending to turn home Rafael's deep cross and make it four.
United swagger through to the quarter-finals after humbling Milan over the two legs, as Rooney yet again established himself as one of the world's most potent attacking forces.