Going down to 10 men and failing to finally beat Chelsea in the Premier League left Arsenal "with a lot of regrets", according to Arsene Wenger, who defended his decision to withdraw Olivier Giroud.
The Gunners have not beaten their rivals from west London in the league since October 2011.
With Arsenal challenging for the title and champions Chelsea, having sacked Wenger's nemesis Jose Mourinho in December, languishing in the wrong half of the table, the match at Emirates Stadium on Sunday was viewed as a perfect opportunity for the hosts to end that sequence.
A red card shown to centre-back Per Mertesacker after just 18 minutes dealt a serious blow to Arsenal's hopes and they proved unable to find a way back after Diego Costa struck the only goal of the game for the visitors five minutes later.
Wenger praised his players for staying in the contest despite their numerical disadvantage but could not disguise his disappointment at passing up a golden opportunity to overcome a lingering psychological hurdle.
"We played with 10 men, we were 1-0 down straight away," he said.
"Normally you lose a game like that three or four-nil.
"We come out [of the game] with a lot of regrets because we feel we couldn't play with our team and looking at Chelsea today there was a lot of room to beat them if we had played with 11 players."
The Arsenal fans made their feelings known when centre-forward Giroud was sacrificed for defender Gabriel Paulista in the 22nd minute to compensate for the departure of Mertesacker.
Wenger did not appreciate being held to account over the enforced change, saying: "Do you want to make a poll after every decision to see who does what?
"I made the decision and for me it was quite a normal decision because we … needed pace to go from one goal to the other."
Asked if Giroud was fit enough to start the match after reportedly struggling with an ankle problem, Wenger said: "I think yes, but it was a bit in my mind - if he gets injured, he didn't practice yesterday, today we declared him fit [but] of course it was on my mind.
"I had to change a player, I thought that was the most rational decision."
The defeat to Chelsea leaves Arsenal third, three points behind leaders Leicester City and two ahead of fourth-placed Tottenham.
