United had started brightly, but didn't look 100 per cent confident as they scrapped for an early breakthrough.
That breakthrough came on 18 minutes as the smallest man on the pitch, Paul Scholes, was allowed a free header in the Sunderland area.
The midfielder rose to connect with a Wayne Rooney cross and headed past stranded Craig Gordon in the home goal.
Many might have expected Sunderland heads to drop, but instead the Wearsiders came fighting back and will have felt unlucky not to have been on level terms at the break.
The home side were almost gifted an equaliser as United defender Nemanja Vidic steered the ball past goalkeeper Ben Foster and just wide of his own net.
The Wearsiders went closer still on 35 minutes as Djibril Cisse brought a great one-handed save out of Foster with a powerful shot.
And Ricky Sbragia's men were then denied by the width of a post. Winger Carlos Edwards crossed from the right and the ball was deflected off the foot of former Black Cats loanee Jonny Evans and on to the far upright, before the danger was cleared.
Sunderland started the second-half slowly and were on the back foot for the early stages.
However, with ten minutes played their endeavour appeared to pay off as they got back on level terms.
Teemu Tainio nutmegged Ji-Sung Park, before crossing to the back post. Kenwyne Jones' initial header came off Evans, but with Foster caught in no-man's land, the Sunderland striker got a second bite of the cherry and hooked the ball into the net.
It was no less than Sunderland deserved and gave the home crowd a massive lift.
The Wearsiders continued to probe away looking to add to their tally but it was United who went closest.
Scholes was just wide with a thunderous effort from 25 yards out and Carlos Tevez just cleared the bar with a free-kick from the edge of the area.
It looked as though the Wearsiders might just hold out and that spurred Manchester United boss Sir Alex Ferguson to ring the changes.
First he turned to world superstar Cristiano Ronaldo, who replaced Park and then Macheda, who came on for the ineffective Dimitar Berbatov.
It was the youngster who made all the difference for United, grabbing them three precious points as the race for the title nears the final stages.
Michael Carrick's 75th minute effort was deflected into the path of the young Italian and he steered it past Gordon in the Sunderland goal to make it 2-1.
After that United seemed happy to play down the clock and despite Sunderland's best efforts to get back into the clash there was no way back.
Relegation still hangs over the Wearsiders, for United though there are no such worries after normal service was resumed.
This was hardly a classic display from the Red Devils, but its points that matter and that's certainly what Macheda delivered with his decisive strike