كتب : وكالات
Anton Ferdinand headed home in the 77th minute to level the score line before Matthew Upson powered another lethal header in the 82nd minute to seal a precious victory.
Ronaldo, who scored United's goal in the 14th minute, missed a penalty when United were one up.
United's tally froze on 45 points, one ahead of Arsenal, who play Everton later on the same day.
Elsewhere, Chelsea beat Newcastle 2-1 thanks to goals from Salomon Kalou and Michael Essien.
Ghana star Essien opened the scoring in the 29th minute when he converted Shaun Wright-Phillips' shot home.
Nicky Butt leveled 11 minutes after re-start but a debatable goal from Kalou secured the three points for Chelsea.
The Ivory Coast striker looked offside when a deflected shot fell into his path but the referee waved the play on.
He rounded Newcastle keeper Shay Given and poked the winner home.