Kompany was given his marching orders in the 10th minute after he hauled down a goal-bound Nikica Jelavic at the KC Stadium.
The visitors shrugged off the setback to win 2-0 courtesy of David Silva's stunning first-half effort and Edin Dzeko's last-minute strike.
Pellegrini conceded that Kompany's foul on Jelavic was worthy of a dismissal but he felt that the Hull striker should have been punished prior to that.
"It's clear that before Vincent's foul there is a foul from Jelavic that the referee didn’t see and didn't whistle for," the Chilean said.
"Of course Vincent's foul is a red card but there was a foul from Jelavic before.
"I don't want to talk about the referee. We won the game and we played very well."
"It was a very good response in a very difficult week," Pellegrini added.
"We just lost against Wigan and against Barcelona and we needed to win today. Playing with one player less was very difficult.
"It was a good performance because we defended well with the ball and without the ball, and we also had three good chances to score. It was a very professional response from the players."
