Arsenal goalkeeper Petr Cech admitted that referee Mark Clattenburg had a clear view of Per Mertesacker's tackle on Diego Costa and showed no hesitation in showing the red card.
The German was given his marching orders in the 18th minute for bringing down Costa after he was clear through on goal.
The Spain international soon put the Blues forward in the game with a 23rd-minute volley, and that proved to be the decisive goal in the all-London clash.
After the 1-0 defeat to his former club, Cech said: "The referee was very close. He had a clear view of the situation and he decided straight away to give a red card.
"There was no hesitation from anyone. We just had to deal with the fact. You just go on.
"He can't change the decision anyway by protesting for three minutes. We had to regroup, we had to make sure that we reorganised and try to continue with 10 men.
"Unfortunately, we conceded too early after the sending off."
