Marcus Rashford scored the winner for Man United but the introductions of Edinson Cavani and Anthony Martial were also key.
Ralf Rangnick confirmed Manchester United switched to a 4-2-4 formation to secure their 93rd-minute winner against West Ham.
United started again in a 4-3-3 formation and remained in it following the like-for-like change of Marcus Rashford for Anthony Elanga.
Rangnick introduced Edinson Cavani and Anthony Martial for Mason Greenwood and midfielder Fred in the final 10 minutes and Bruno Fernandes dropped back to partner Scott McTominay. All three substitutes combined for the winning goal.
Deep into the second-half, one of the West Ham analysts complained Ronaldo was 'killing us in that pocket' and Ronaldo's deep position for the winner drew two defenders and freed up space for Cavani and Martial down the left.
United have played in 4-2-2-2, with a back three, 4-2-3-1, 4-3-3 and 4-2-4 in their last four games, with Rangnick changing formation in the second-half.
The German was thrilled United's risk-taking paid off. "If you include Cristiano, who was also involved, all four strikers that were on the pitch, we played in a 4-2-4 with four strikers. All four strikers were involved, well done and a great moment for the club and the players.
"In the last 20 minutes, we had two or three shots from outside the 16-yard box when there was not a realistic chance to score or hit the goal. I wished our strikers had played that vertical ball into the box, we didn't always make the right decisions in the final third, but it is something we have to improve, develop and with this win it's easier than if it was a draw.
"Defensively, one of the best performances in the last two months. On the ball, I'm still not quite happy with how we are playing."