The 28-year-old struck the only goal of the game at Old Trafford to pull the Black Cats within touching distance of safety.
"Goals have been way too far apart for me lately; I'm used to scoring a lot more," Larsson told the club's official website after the game. "It's took its time to come but I suppose it was a good time to score.
"We defended very well throughout the game and we knew we'd have to do that. Towards the end we had spells where we passed the ball nicely and hit the woodwork twice, so overall I think we deserved the win."
The victory lifts Sunderland three points clear of Norwich who occupy the final relegation spot.