But United boss Ferguson, who was forced to watch from the stands, went all out attack as a quickfire Rooney hat-trick and a Javier Hernandez strike sealed the three points.
And his star striker credited the introductions of the little Mexican and Dimitar Berbabtov for helping turn the game.
He said: “Berbatov was fantastic for us holding up the ball and making things happen.
“The substitutions were good substitutions and they won us the game.”
Ryan Giggs, who moved to left-back in the second half, put the victory down to United’s never-say-die attitude.
He said: “In the first half we played some good stuff and gave silly goals away.
“We felt that if we kept going and got a goal we knew we could do it. We dont give up, no matter what the score.
“We were brilliant all over the park but even when he haven’t been playing well we have been grinding out results.”With Ferguson banned from the touchline, the first chance he got to talk to his players came at half-time.
But even at 2-0 down Giggs insisted the United boss was not angry with the team.
The veteran said: “He was calm because we were playing well.
“We just got into some good areas and the final ball wasn’t good enough, we knew the goals would come.”
West Ham boss Avram Grant was deflated after the game, but insisted his side could bounce back.
Asked whether the the defeat could affect morale, Grant replied: “It will not damage it.
“We are a strong team and we have showed we can recover well.
“We are disappointed. It was 2-0, we played well and then they scored.”
The result saw the Hammers slide back into the relegation zone, but Grant would not read too much into the loss.
He added: “We had a big job before. We can get over this.
“We came strong, we were very good in the first half and it is more disappointing.”