United were fortunate to be level at 1-1 before the England striker headed two second-half goals.
"It's devastating form, they just couldn't handle him second half. I thought he was marvellous," United manager Ferguson told a news conference before being asked to compare Rooney to the likes of Lionel Messi and Cristiano Ronaldo.
"His basic ability is as good as the players you talk about. What we said he has to do is improve his goalscoring and now that he is... he must be regarded alongside these players."
ANALYSIS: Old legs and young Mister taught harsh lesson by youngsters and a guru
Seven-times champions Milan took an early lead through Ronaldinho and really should have at least doubled their advantage before Paul Scholes equalised with a fluke goal that hit his standing leg nine minutes before the break.
Clarence Seedorf pulled one back for the hosts five minutes from time and United's Michael Carrick was sent off for two bookings in injury time meaning he will miss the second leg on March 10.
"I think we could have lost a few goals tonight. The first 20 minutes was a bad period for us. For 20 minutes we lost composure. Once we got going, we played well," Ferguson said.
"We could have been two or three down. But I don't think it was fortunate."
Milan's rookie boss Leonardo disagreed with Ferguson and felt United had been lucky.
"I think we didn't score the goals we deserved. Manchester United managed to take 100 percent of their chances," the Brazilian said, ruing several chances which only just missed.
"It's a question of centimetres unfortunately. You can't play 90 minutes at the same rhythm we started the game with. I can't criticise my side. Scholes' was a very lucky goal.
"I don't think to win 2-0 at Old Trafford is a totally impossible thing."
WIN: Tickets for Manchester United vs AC Milan
‘He instantly popped into our ratings as one of the best U21 midfielders in Europe. The impressive thing is Slot has made him into more of a no.6' Inside Ryan Gravenberch's transformation at Liverpool
‘I don’t think Liverpool would look at Ollie Watkins, a striker isn’t a pressing issue for them – it’s Arsenal who need one’ Former Reds star explains why his old club don’t need an out-and-out forward this summer
