Manchester United 2 FC Porto 2 There were last-gasp heroics again, but this time Manchester United were on the receiving end as Porto cast a major doubt over the Champions League holders retaining their European crown.

Sir Alex Ferguson had waxed lyrical in the build-up to this contest about how Sunday's dramatic late winner against Aston Villa had "galvanised" his club. Yet there was little evidence of that last night, and the only things likely to have been galvanised at Old Trafford were the tin helmets being prepared for Ferguson's post-match tongue-lashing of his players.

This was one of the least convincing Champions League displays by United at home in recent times, and the scoreline perhaps flattered the European champions. The advantage of the away goal could yet prove crucial to Porto.

Ferguson's suggestion that Federico Macheda's amazing goal against Villa will be a turning point looks equally unconvincing. Few United players emerged with credit from this draw and only Wayne Rooney's predatory instincts turned a looming disaster into a mere disappointment. Two away goals for Porto is still a huge and unexpected bonus for the Portuguese side.

Certainly, for those clubs who still have to face United in any competition during the remainder of this season, the lesson from this seems clear - fortune favours the brave.

From the off Porto had clearly decided that attack was the best form of defence, and that was something of a treat for any neutral who had turned up expecting a dreary battle between two sides wary of risking anything.

Lisandro had already had a viciously swerving shot turned over by Edwin van der Sar when Cristian Rodriguez capitalised on two woeful pieces of United play to open the scoring in the fourth minute. Cristiano Ronaldo, who had another match to forget, gave the ball away first. Jonny Evans was given a second chance but his clearance went straight to Rodriguez, and he sidestepped the Northern Ireland defender before curling the ball low to Van der Sar's right.

Confidence flowed through Porto as though the sluice gates had been opened and Ferguson's men could easily have been two down before the equaliser arrived. More clinical opponents would have already dealt United a fatal blow - as it was, Rooney showed that a wounded animal can be the most dangerous.

Bruno Alves, perhaps Porto's most highly-rated player, was guilty of an error of such magnitude that even a schoolboy would have been embarrassed. Rooney's natural instinct made him run to anticipate the back-pass and he knocked it over the stranded Helton.

Anyone would have expected such a gift to deflate the Portuguese side. Instead, it was United who continued to look rattled while Porto, inspired by the impressively-named Hulk, struck fear into United's defence.

Suspicions that a half-time hairdryer to swing the match United's way was destined to be disappointed as Porto continued to break at speed and Van der Sar made another very good save to keep out Lisandro again.

Hulk had a convincing penalty claim against Carlos Tevez before the substitute struck with five minutes to go, after a clever flick by Rooney, to apparently hand United an undeserved victory but Porto's good work was not in vain as in injury time Lucho's cross from the right found substitute Gonzalez in acres of space at the far post and he took his time before stabbing home.

It will be a daunting second leg for United now, and Ferguson will know that down the East Lancs Road, Rafael Benitez would have been smiling.

The smarting Scot slammed his side's lack of concentration. "The result was about right. In the first half, they were the better side but we improved in the second and got more possession," he said. "But getting the second goal the way they did, we should really have defended that. It was a bad goal to lose.

"It's been a hard two days for them after playing Aston Villa on Sunday, but they were lacking in concentration."

Ferguson, who revealed Evans had limped out with a groin injury, added: "If you get a 2-1 lead with four or five minutes left, you really should see it out. We've got a game on Saturday at Sunderland, there's still a lot going for us, but it will be a difficult game now in Porto. No question of that."