Arsene Wenger said the decision to send off Per Mertesacker against Chelsea was "very harsh" and that Diego Costa had been "clever" in drawing another red card against the Gunners.
Arsenal were reduced to 10 men in the 18th minute when Mertesacker went in for a clumsy challenge on Costa, who went to ground despite what appeared to be light contact. The German defender was given a straight red card for a last-man foul and Costa scored the winning goal shortly afterward.
In the teams' first meeting at Stamford Bridge this season, Arsenal defender Gabriel Paulista was sent off for retaliating against Costa after a scuffle and Chelsea won 2-0.
"Costa got two players off in two games on our side, so he's clever," Wenger told Sky Sports after the game. "In the first game he got Gabriel sent off and today he got Mertesacker sent off with a tackle, regular or not. Did he touch him or not? I have to watch it again. But the fact is a fact, I do not accuse him of anything, it's just what happened."
In a separate interview with the BBC, Wenger said referee Mark Clattenburg had been "very quick" to take his red card out after the challenge.
"I think it was a very harsh decision. But we had to cope with it. I do not know exactly what to say, because it's a few games now that that happens [with Costa]," said Wenger, who this week had stressed the importance of showing discipline when dealing with the Chelsea striker.
Asked if Costa had made the most of the opportunity, Wenger said: "That's a bit the game of a striker, and Diego Costa is good at that as well."
Wenger said he was pleased with the way his team responded to going a man down but was left ruing a number of missed chances to equalise.
"It's a shame to put such an energy level into a game and come out without a point. Overall I felt that we gave absolutely everything until the end. We should come out of the game with at least a 1-1 even down to 10 men," Wenger said.
"We had many opportunities, maybe not clear-cut but you think one of them we should take. That's a regret, that the team put in so much energy and we come out without any point. Of course we had a mountain to climb with 10 men, but even there I believe that there was enough room there to come out with at least a 1-1."
The loss leaves Arsenal three points behind new leader Leicester and behind Manchester City on goal difference. The team have taken just two points from their last three games. But Wenger said his views on the title race had not been affected by Sunday's result.
"It hasn't changed, that it will be very tight until the end and that you will have many teams involved in it," Wenger said. "But today was a home game, and we knew that it was very important to win the big games like that. So we focus on the next one."