FA Cup/ Manchester Utd 2 Aston Villa 1: This was the day Henrik Larsson showed that he could be one of Alex Ferguson's cannier signings - and Ole Gunnar Solskjaer proved that, when it comes to Scandinavian strikers, there is still nobody to touch him at Old Trafford.

Larsson will cherish the memories, but it was Solskjaer's contribution in stoppage-time that was decisive for Manchester United, aided by the kind of goalkeeping error that may have Gabor Kiraly waking in cold sweats for weeks to come.

Trailing to a splendid debut goal from Larsson, Villa seemed destined for a replay courtesy of a 74th-minute equaliser from Milan Baros, their substitute striker. United had been on top for most of the game, but droves of supporters were already heading away believing Villa's performance had been dogged enough to add another match to the club's winter schedule.

But then came injury time. Wayne Rooney played in Solskjaer and, coming in from the right, the Norwegian lashed in a shot that, though well struck, ought to have been a routine save for Kiraly. Horribly, inexplicably, the on-loan Crystal Palace goalkeeper got his positioning all wrong. The ball squirted through his arms, dribbling almost apologetically into the net, and suddenly it was Ferguson on the touchline, in his classic pose, pointing at his watch and haranguing referee Martin Atkinson to blow the final whistle.

Martin O'Neill, the Villa manager, was sensitive enough not to blame Kiraly, a goalkeeper he signed as emergency cover because Thomas Sorensen and Stuart Taylor were injured, but the mistake was so bad even Solskjaer looked vaguely embarrassed.

"We're all disappointed, but Gabor is distraught," said O'Neill. "It's bitterly disappointing because we had done so much to get back in the game. He was feeling pretty good at half-time because he had made one or two good saves, but that's the way it can go when you're in goal."

It was certainly a cruel way for Villa to go out, yet Ferguson was entitled to argue it was merited on the balance of play. "I think we deserved to go through because the number of chances we created was terrific," he said. "I was thinking about it being a replay and wondering whether Villa might sign anyone beforehand. But with Ole on the pitch you know you've always got a chance of scoring."

Rooney, in particular, will be indebted to Solskjaer's knack of scoring late, decisive goals. The England striker had another difficult afternoon and was fortunate to get away with a couple of off-the-ball kicks, first at Gavin McCann and then Liam Ridgewell, with the score at 1-1. Had he been feeling vindictive, O'Neill might even have argued that the man who would go on to set up the decisive goal should have been sent off.

O'Neill has too much dignity to resort to such accusations, however, and preferred instead to reserve his post-match comments to praising his players. McCann, a midfielder with everything but pace, was outstanding, all sweat and crunching tackles. Isaiah Osbourne, an exciting 19-year-old, was not far behind, and United's frustrations in the first half could be gauged by the sight of Ferguson charging from his dugout to unleash a stream of invective at Ryan Giggs.

What the game desperately needed was something to lift the decibel levels, and Larsson provided it 10 minutes into the second half. Busy and effective throughout, the 35-year-old Swede had been denied only by Kiraly's right boot when he ran through, one-on-one, late in the first half.

The chance he scored from was more difficult, and Larsson's finish, with the minimum back-lift, was so skilful it should have silenced any doubts about whether he can have a significant impact on English football.

Giggs, increasingly influential, whipped a free-kick on to the top of Kiraly's crossbar a few minutes later, but Villa are a resilient side and Baros's equaliser was their reward for a sustained flurry of pressure.

"We played our best football after we had gone behind," O'Neill would later say.

Or to put it another way, after he had taken off the dismal Juan Pablo Angel. More players were committed to attack and Baros made it count when he intercepted Gary Cahill's shot and placed the ball beyond Tomasz Kuszczak.

Ferguson, a week into life as an OAP, responded by replacing his oldest outfield player with the second oldest. Solskjaer shook Larsson's hand, then set about doing what he does best.

Of his temporary signing, Ferguson said: "I think he will score important goals for us. He's done that all throughout his career. I said the same about Eric Cantona; that he always seemed to score important goals and winning goals.

"I wanted to find out about his fitness and sharpness and he's proved that," said the United manager. "His split-second movement, experience and judgment of when to run and not to run were terrific."

O'Neill was familiar with all of this. "When I was in Scotland, people asked me, 'Could Henrik score goals outside of Scotland?' said O'Neill. "I never thought for one moment that he couldn't score in any league that he chose. I think he's gone on to show that."

• Guardian Service