Trailing at the break as their defensive frailties finally caught up with them, there appeared to be no way back for a United side playing second fiddle to brilliant Brazilian Kaka.

But amid the debate over who is currently the world's best between Kaka and Cristiano Ronaldo, England's young genius forced himself back onto centre stage, driving the Red Devils level when he darted onto Paul Scholes inspired pass before drilling home a superb injury-time effort after Ryan Giggs had led a late charge forward.

It leaves Alex Ferguson's men just needing to avoid defeat in the San Siro next Wednesday to confirm an all-English Final in Athens on May 23.

The victory was all the more remarkable given the hosts were outplayed at times by a mesmeric Milan outfit, who bounced back in superb style from Ronaldo's fourth-minute opener and were never likely to be the powderpuff opposition Roma provided in the last round.

Ferguson had warned the home supporters there would be no repeat of the seven-goal rout of a fortnight ago, and so it proved.

But for a few precious minutes, United dared to believe after making the same rapid start which set them on their way that stupendous victory.

Ronaldo rose to meet Ryan Giggs' corner, saw his firm header strike the Milan keeper in the shoulder, then, as Gabriel Heinze closed in on a looping ball that might have been dropping over the line anyway, Dida pushed it in.

Old Trafford erupted, temporarily forgetting the mass of players absent, hoping and praying the lead could be held, or even built upon.

Who knows what might have happened had Michael Carrick volleyed home an astute chipped cross from Giggs as Ferguson's men pushed forward enthusiastically looking for a second.

As it was, a strangely out of sorts Carrick mis-hit his shot and Dida parried it away. It was precisely the type of opportunity Ferguson had implored his side to take. And by the time they got another one, Milan were in the lead.

Iti did not last too long, however. The free-kick given against Darren Fletcher from which Milan fashioned their equaliser was a harsh call, but once the ball arrived at Clarence Seedorf's feet, United were in trouble.

Seedorf, a winner in this competition with three different clubs, spotted Kaka's determined run and slid a perfect pass into the Brazilian's feet which allowed him to gain a precious half-yard on Heinze and flick his shot into the far corner.

The coolness of that effort was repeated 15 minutes later when a catastrophic collision between Heinze and Patrice Evra offered Kaka a free run on the United goal which ended with an emphatic finish.

Evra had been a major doubt beforehand and the Frenchman probably wished he had not bothered when he picked up a booking late in the half that will rule him out of the second leg.

United's second-half salvage operation should have begun perfectly when Giggs' corner fell to an unmarked Carrick at the far post.

Twice a scorer against Roma, the former Tottenham man could only hold his head in his hands as he missed again.

With Milan's intricate passing truly magnificent, it seemed only a matter of time before Kaka would complete his hat-trick and seal the tie.

Yet even in this ravaged state, United are still capable of sublime moments of skill and Scholes promptly produced one, lofting a pass over the Milan defence from a standing position which invited Rooney's fierce finish.

Once more, Ferguson's side banished the demons created by their shattered defence. Dida pushed away a piledriver from the outstanding Fletcher. Ryan Giggs twice went close.

It seemed they would have to settle for a draw but Milan reckoned without Rooney.

Largely ignored amid the welter of publicity for Ronaldo this season, the 21-year-old has now caught his young-team mate on 22 goals. And how precious his latest effort could prove to be.