London - Arsenal manager Arsene Wenger dismissed suggestions that his side have a mental block regarding London rivals Chelsea following a 1-0 home defeat that carried an air of deja vu.
Arsenal were bidding to return to the top of the Premier League table in Sunday's game, but they were left in third place after Per Mertesacker was sent off and Diego Costa scored to give Chelsea a clinical 1-0 victory.
Arsenal have not beaten Chelsea in nine league games and have not scored against them in the league in nine hours and 32 minutes, but Wenger said that Mertesacker's 18th-minute dismissal, for a last-man foul on Costa, meant it impossible to compare the game with previous fixtures.
"I think today (Sunday) was a special game. We played with 10 men, we were 1-0 down straight away. Normally you lose a game like that 3-0 or 4-0," he told reporters at the Emirates Stadium.
"When you have to chase the game, (there's) nothing more dangerous than being down to 10 men. Overall we come out with a lot of regret because we feel we couldn't play with our team.
"And looking at Chelsea today, I think there was a lot of room to beat them if we had played with 11 players."
Mertesacker was shown a straight red card for felling Costa after he had latched onto a through-ball from Willian.
The Chelsea striker immediately made his side's numerical advantage count by converting Branislav Ivanovic's cross with a near-post volley in the 23rd minute.
Costa had goaded Gabriel into kicking out at him in September's reverse fixture, earning the Arsenal centre-back a red card, and Wenger told a TV interviewer: "He has got two (Arsenal) players sent off this season."
Addressing the print media shortly after, the Arsenal manager backtracked, saying that he had only been stating "facts", but maintained that referee Mark Clattenburg's decision had been "harsh".
Chelsea's interim manager Guus Hiddink said that Mertesacker's lunge had merited "a red card without any discussion".