The England goalkeeper kept out his national teammate early in the second half after bringing down Demba Ba in the area and Benitez suggests that moment turned the game in City's favour as they eventually ran out two-goal winners thanks to Yaya Toure and substitute Carlos Tevez.
"I haven't seen the replay, but at least yellow card," the Spaniard said.
"You can argue he is going in this direction but it is still a clear chance.
"I think it was a turning point. We didn't do well in the first half but we went to half-time at 0-0.
"We were talking about keeping the ball, doing better and showing more character. Then we had the penalty. It was a crucial moment in the game."