Having been benched for the draw to Chelsea at the weekend, the 36-year-old showed he's still got plenty to give with an assured finish and an emphatic penalty helping seal Man United the win with Ralf Rangnick watching on in the stands.
The Red Devils went behind when Emile Smith Rowe fired into a near empty net with David de Gea down injured in the United goal, however, the goal was awarded as the goalkeeper was hurt by teammate Fred accidentally standing on him.
Bruno Fernandes levelled the scores just before half time and Portuguese compatriot Ronaldo put Man United in front early in the second half.
Martin Odegaard hit straight back for Arsenal but the Norwegian became the villain as his foul on Fred gave Man United the chance to retake the lead.
Ronaldo made no mistake as he smashed the ball down the middle, taking his professional goal tally to an incredible 801.
Michael Carrick, in charge for the final time as caretaker boss before Rangnick takes the reins, started Ronaldo this time but the hosts made a slow start to the match.
The Gunners had the ball in the net on 13 minutes but it looked like Smith Rowe's strike wasn't going to be given with De Gea writhing in pain on the floor. However, after plenty of deliberation it was awarded as the Spaniard's injury was self-inflicted with Fred accidentally treading on his foot.
United were largely restricted to long-range pot shots until the 45th minute when Fernandes slotted in the equaliser after good inter-play from Jadon Sancho and Fred.
It was 1-1 at half time but Arsenal were perhaps unlucky not to get a penalty with Harry Maguire appearing to pull Takehiro Tomiyasu down in the box in stoppage-time.
There was an explosive start to the second half with both sides going close but Man United went 2-1 up on 53 minutes when Ronaldo slotted in Marcus Rashford's pull back following a mistake from Nuno Tavares.
But quick as a flash it was 2-2 when Odegaard scored a similar goal as he slotted Gabriel Martinelli's cross from the right, the ball trickling past De Gea.
Pierre-Emerick Aubameyang stung the palms of De Gea as both sides searched for the winner, which went to Man United.
After a pitchside review, Martin Atkinson penalised Odegaard for felling Fred in the box and Ronaldo smashed the resulting penalty straight down the middle of Aaron Ramsdale's goal.