Arsene Wenger bemoaned the influence of Diego Costa as the Chelsea striker once again proved a thorn in 10-man Arsenal's side.
Costa in September tussled with Laurent Koscielny and Gabriel, who was sent off, and on Sunday drew a foul from Per Mertesacker which saw the German dismissed at the Emirates Stadium in Chelsea's 1-0 win.
The Chelsea striker then netted his sixth goal in six games to dent the Gunners' title hopes and extend their winless league run against their London rivals to nine games.
Wenger told Sky Sports 1: "Mertesacker made the challenge but I said he got Mertesacker sent off, you can not say it's not true.
"I haven't seen it again, I said in the first game he got Gabriel sent off and today he got Mertesacker sent off. A fact is a fact, I do not accuse him of anything, it's just what happened."
Asked about the incident later in his post-match press conference, Wenger said: "I said Costa got two of our players sent off in the last two games against Chelsea. Those are only facts.
"Is the decision right or wrong? I don't know. That is a fact, without accusing him of anything."
Wenger had not seen the incident again nor spoken to Mertesacker, but described referee Mark Clattenburg's decision in the 18th minute as "quick and harsh".
"The referee made a decision and we have to get on with it," Wenger said.
"I didn't know if Costa was offside or not, or if Per Mertesacker touched him or not. I don't know.
"It was of course frustrating, but it's a decision we have to take on the chin and get on with our job. That's what we did."
The Frenchman declined to address Costa's role further, but rued his side's inability to make the most of the opportunity against a Chelsea side whose title defence has fallen apart this season.
"I would not compare today's situation," Wenger said.
"It was not a confrontational situation like it was at Chelsea.
"It was a fact of a game and a decision of a referee. I don't think it was linked with any bad behaviour or attitude.
"We come out with a lot of regrets because we couldn't play with our (full) team, and looking at Chelsea today, there was a lot of room to beat them if we had played with 11 players."
Wenger praised his team, despite a fifth loss of the season which leaves them three points behind Leicester in third place.
"Despite the disappointing result, we should have even more belief in ourselves after the game," Wenger said.
"The team were focused and resilient, fighting to the last second."
Striker Olivier Giroud was sacrificed for defender Gabriel after Mertesacker's dismissal, a decision greeted by boos from Gunners fans.
"Do you want to make a poll for every decision to see who does what?" Wenger said.
"I made the decision and, for me, it was quite a normal decision. We knew we had to drop deeper and to use pace to get forward."
Chelsea interim boss Guus Hiddink is now unbeaten in seven matches and the Blues undefeated in eight since Jose Mourinho's departure last month.
Captain John Terry believes a top-four place and Champions League qualification is not beyond the team, despite a 14-point gap to fourth-placed Tottenham with 15 games to go.
Hiddink said: "With that gap, it's difficult to go into fourth position. But when the captain is saying that I will follow my captain."
Hiddink described the sending off as "obvious" and rued the decision to deny Cesc Fabregas a penalty when Koscielny body-checked the playmaker.
"There was no doubt. From what I saw (Costa) was tripped," Hiddink said.
"I had some doubts over the Fabregas penalty, yes or no. I can understand why the referee didn't give a penalty, fair enough.
"But on Mertesacker's red card, look closely. It was obvious I think."
Costa was withdrawn in the second half with a knee problem, but Hiddink did not know the extent of the injury.