Arsene Wenger felt match-winner Diego Costa was "clever" in the incident that saw Arsenal reduced to 10 men during the 1-0 home reverse to Chelsea in the Premier League.
Per Mertesacker was sent off after 18 minutes for bringing down Costa as he raced towards goal, before the Spain international scored what proved to be the only goal of the game at Emirates Stadium five minutes later.
Sunday's events came after Arsenal were reduced to nine men in the 2-0 loss to Chelsea at Stamford Bridge in September, when Gabriel was controversially removed for clashing with Costa, before Santi Cazorla's red saw the Gunners finish with nine men.
Wenger was pleased with the way his team battled after Mertesacker's dismissal, but felt referee Mark Clattenburg was taken in by Costa.
"He [Clattenburg] had the choice, of course he had the choice, he made the decision, I cannot influence the decision and we coped well and got on with our job," the Frenchman told Sky Sports.
"We cannot influence the decision of the referee, Costa got two players off in two games for our side, so he is clever."
Asked whether Costa got Mertesacker sent off, Wenger replied: "Yes, of course.
"Yes, Mertesacker made the challenge, but I say he got Mertesacker sent off. I have not seen it again.
"In the first game he got Gabriel sent off and he got Mertesacker sent off. Did he touch him or not? I have to watch it again. Fact is a fact – I do not accuse him of anything, it is just what happened."
The result means Arsenal remain three points behind leaders Leicester City in third place, with Wenger believing his team deserved at least a draw.
He added: "The disappointment is there, but what is important is the points rather than emotional damage.
"We should have come out with at least a 1-1 - even down to 10 men. That is the regret, we put so much in and come out without a point. We had a mountain to climb with 10 men but even then there was enough to come out with a 1-1.
"It [the title race] will be very tight until the end and many teams will be involved in it. We focus on the next one, but it is a shame to put such energy into a game and come out without the points."