The Reds finally got back to winning ways in the Champions League after four successive draws to claim a place in the quarter finals of the competition.
The result was not as convincing as might appear as Inter Milan pushed them all the way, hitting the woodwork twice and wasting some clear cut chances just before the break.
When Nemanja Vidic was allowed to rise unchallenged and head home Michael Carrick's corner after only four minutes it seemed that Manchester United were on their way to a comfortable victory over Inter Milan.
But instead of building on this ideal start United slowed the pace down which suited a rattled Milan and allowed the visitors to regroup and finish the half strongly.
The Reds became sloppy in their passing and lacked the cutting edge when they approached the Milan goal.
The warning signs came on 30 minutes when Milan's Zlatan Ibrahimovic was allowed to meet a free kick, but his downward header clipped off the top of the bar.
As the half closed the United goal enjoyed a charmed life. Twice Dejan Stankovic went close, first from 30 yards and then when it seemed easier to score.
Ibrahimovic was allowed to break clear against a hesitant Reds defence and flash a shot across the face of Edwin van der Sar's goal.
Yet during this uncertain spell in which Milan dominated, United should have doubled their advantage.
Wayne Rooney combined with John O'Shea but the Irishman allowed Julio Cesar to block his effort from close range.
Inter began the second period as they ended the first, in the ascendancy.
Mario Balotelli hammers a shot wide, but almost immediately the visitors find themselves two down.
Rooney collects the ball from Ryan Giggs, bides his time, before chipping into the middle of the penalty area for Ronaldo arriving late, and unmarked, to head past a stranded Cesar.
The lively start to the half continued with substitute Adriano almost pulling a goal back with an acrobatic volley which rebounded off the post.
But United hit back and Dimitar Berbatov and Rooney both went close as the game began to open up.
United were content to simply soak up the Milan pressure which became more desperate as the time ticked down.
Yet in the end United's finishing proved decisive against the profligate strikers of Milan.
After the game Inter boss Jose Mourinho continued his feud with the Italian media.
"All of Italy will be happy that Inter went out. I don't care, though. I know that I won," said Mourinho.
"I am not angry, just sad. Before laying a finger on my team, they have to go over my dead body.
"We did not have the luck that is needed to win these big games. It's a shame for those who had never won this trophy and wanted to achieve that.
"If Inter had a problem of fear towards the Champions League, then tonight they proved that it is no longer an issue.
"We are missing something, but I will explain that to the club. In any case, now we will absolutely without doubt win the Scudetto."