Paul Scholes' dismissal for two yellow cards after just 33 minutes left the Red Devils in trouble.

For a brief period after Rooney had coolly levelled Taddei's first-half strike, it appeared United would complete their mission with spectacular success.

But substitute Mirko Vucinic bundled home the rebound after Edwin van der Sar had failed to hold Mancini's blistering shot to earn Roma a richly-deserved victory.

At least Sir Alex Ferguson got the away goal he demanded but the United boss knows his side, lacking the suspended Scholes, will have to do better in the return leg on Tuesday to stand any chance of progressing to the last four.

Ferguson had promised every tactical angle would be covered as United attempted to reach the semi-finals for the first time since 2002.

In terms of shackling dangermen Francesco Totti and Mancini, the visitors largely got it right.

Unfortunately, they failed to heed early warnings about Roma's liking for quickly-taken corners and eventually paid the price.

Van der Sar might have fancied his chances of keeping out Taddei's effort. But once it flicked off Wes Brown and Gabriel Heinze, the giant Dutchman had no chance.

It was a goal Roma definitely deserved but unfortunately, it sparked ugly scenes in the stands where, for the second United European away-day running, riot police were called in to quell disturbances.

Prior to the encounter in the Italian capital, five United supporters were hurt during clashes with home fans in the vicinity of the stadium.

An estimated 4,000 United supporters who made the trip to the Eternal City took their seats two hours prior to kick-off but both sets of supporters threw missiles before the start of the game and the tension soon returned after Scholes was sent off.

Trouble escalated after Roma took their 43rd-minute lead, with Italian police storming the United fans section using batons against them before calling for reinforcements.

Announcements made in both English and Italian continued to be aired during half-time, warning fans the game could be abandoned if the violence continued.

Tensions died down after the restart and the game ended with no further trouble, with the visiting fans escorted out of the stadium 90 minutes after the final whistle.

Apart from their team going behind, United's 4,000-strong travelling support were also taking in the fact their team had been totally outplayed and were down to 10 men following Scholes' dismissal.

Never the best tackler, the former England star had already ruled himself out of the Old Trafford return by flying into Christian Wilhelmsson on the halfway line.

When he then stuck out a leg to halt Totti's advance, German referee Herbert Fandel had little alternative other than to brandish a second yellow card.

The dismissal just gave Roma even more licence to attack. Totti brought a couple of good saves out of Van der Sar, then Taddei did the same to earn the corner that eventually led to his goal.

In fact, with Cristiano Ronaldo and Rooney completely snuffed out and Ole Gunnar Solskjaer making little impact either after being handed the central striker's berth, about the only thing that went right for United in the opening period was the booking Simone Perrotta picked up for diving under Heinze's challenge when the tie was still level.

It must have been particularly disappointing for Perrotta, one of three World Cup winners in the hosts line-up, as it ended his hopes of an emotional return to the city of his birth, having been raised in Ashton-under-Lyme before his parents returned to Italy when he was a child.

The Roma onslaught continued once the game re-started but, with Perrotta twice failing to add to the home side's tally, there must have been some lingering suspicion within the Roma camp that a nasty shock was awaiting them.

And so it proved too as Ronaldo finally escaped the shackles of Roma's rigid defence and found Solskjaer with a superb pass.

The Norwegian instantly lifted a far-post cross to Rooney, who gleefully lashed home his first Champions League goal since his debut-day hat-trick against Fenerbahce in September 2004.

For a few short minutes, an unlikely victory appeared on the cards, with Solskjaer bringing a good save out of Doni as United pressed.

But it proved to be a brief renaissance as Roma quickly regained the initiative after Van der Sar could only beat away Mancini's powerful drive, allowing substitute Vucinic to force home the rebound.

It was all defensive hands to the pump for the visitors after that.

Perrotta's shot deflected wide off Brown, then the midfielder rasped another just over before Totti flashed a long-range effort just wide when Van der Sar appeared to be beaten.

Heinze was needlessly booked for too much backchat, although at least the visitors were able to run the clock down and escape with a single-goal defeat when it could - and should - have been worse.

"Considering we played with 10 men, mostly against 12 men for an hour, it's a good result for us," Ferguson said after the match.

"I don't think we got a decision all night but that's European football, I'm afraid.

"The referee told us before the game, anyone encouraging players to be booked or sent off, he would book them. But he didn't book the players clapping him, applauding him for sending a player off. So that's not acceptable.

"I can't complain about the sending off. It was probably two cards.

"Paul likes to tackle. Unfortunately in Europe, it's not acceptable."

Scholes will now miss the second leg, and Ferguson added: "We could do without that. We need a full squad of players."

Ferguson was nevertheless pleased with the way his side responded to the dismissal, especially scoring a crucial away goal.

"I said before the game if we score then we have a massive chance," he said.

"At Old Trafford, we've got a fantastic chance, don't worry about that."

Rooney described the match as "one of the hardest games I've played in".

He added: "It was a tough job but we're happy with the result in the end.

"We knew, once we got the goal, it's going to be a difficult game for them coming to Old Trafford.

"It's as good as a 0-0 so it's not a bad position to be in.

"They're a good team, pass the ball really well and they like to create chances.

"We know it's going to be a difficult game but we've got the home advantage."

Rooney insists he felt under no pressure to end his scoring drought in European football, adding: "We're in the quarter-finals of the Champions League, pushing to be in the semi-finals."