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."
The result provided the visitors with the perfect tonic following a week of woe that saw them dumped out of the FA Cup and UEFA Champions League in the space of four days.
"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."
