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".

- 'Follow the captain' -

Wenger reacted to Mertesacker's dismissal by sending Gabriel on for striker Olivier Giroud, which drew a chorus of boos from the home supporters.

But he was unrepentant, saying: "Do you want to make a poll for every decision to see who does what? I make the decision and for me it was a normal decision."

While Arsenal were left three points below leaders Leicester City, Chelsea put seven points between themselves and the bottom three to ease any worst-case-scenario relegation fears that their fans may be harbouring.

The champions, unbeaten in seven league games since Jose Mourinho's dismissal, remain 14 points below the top four, but captain John Terry said that Champions League qualification was still "doable".

"If the captain says yes, then we'll follow the captain! You always follow the captain," Hiddink said in response.

"It's a gap. If you see the results in the Premier League, you see how competitive all the teams are, whether you're down at the bottom or high in the ranking.

"All teams can beat all teams. With this gap, it's difficult to go into fourth position, but when the captain is saying that, I will follow my captain."

Hiddink also revealed that Costa, withdrawn in the 68th minute, would undergo tests on a knee injury.

"I don't know if it's slight or more severe, but we'll check on it," said the Dutchman. "It was a little bit on the knee."

Arsenal host second-tier Burnley in the FA Cup at the weekend before resuming their title challenge at home to Southampton on February 2 and Wenger said that time was on his team's side.

"There is a long way to go," said the Frenchman, who welcomed Alexis Sanchez back after two months out with a hamstring injury.

"What we take from today is that we are disappointed, but have a lot of positives from our attitude and spirit."