United were 2-1 winners at Old Trafford, but they were forced to do it the hard way as Rooney went from hero to villain after lashing out at Stewart Downing on the hour-mark.
After opening the scoring for United in the fifth minute - becoming the Premier League's third highest scorer of all time - Rooney almost cost his team-mates victory when he kicked down Downing, who was attempting to break on the counter-attack.
Rooney decided against appealing the three-match ban, meaning he will miss October's Premier League fixtures against Everton, West Brom and Chelsea.
"It was probably the right decision," said the 28-year-old.
"I saw the West Ham player making a counter-attack and I tried to break up the play, but I just misjudged it.
"I didn't absolutely volley the lad. I tried to trip him up and, to be fair to him, he got further away from me and that's why my leg is straighter than it should have been.
"As he pushed the ball away, my leg straightened out and that is obviously why the referee deemed it as a red card."
Rooney added: "I think everyone knew [I was in the wrong].
"It's always tough against 11 men when you are a man down, especially when they are throwing a lot of balls into the box as West Ham were doing, so I am grateful that we held out."
