Ronaldo used both hands to deflect the ball as it headed towards his face from a Wayne Rooney corner in the second half and was duly sent off by referee Howard Webb.
"He was trying to protect himself from the ball hitting him in the face," said the United boss.
"He thought he had heard a whistle, he got a little push as well and it is not as if he punched the ball.
"If that had been outside the box it would have been a free-kick and nothing else. But the crowd played a part and he got sent off.
"Sometimes you have to overcome these things and we overcame a lot."