Arsene Wenger says he substituted Olivier Giroud against Chelsea because he felt Arsenal “needed pace” to turn defence into attack.
Per Mertesacker was dismissed after just 18 minutes for fouling Diego Costa at Emirates Stadium on Sunday, with Wenger bringing on Gabriel Paulista four minutes later in place of Giroud.
It was a decision which was greeted by boos from the home supporters, but Wenger felt it was the obvious change to make in the circumstances.
“I make the decisions and, for me, it was quite a normal decision because we needed pace to go long distances, to go from one goal to the other,” Wenger said. “We needed to use pace to go forward.
“His ankle was a bit in my mind. He hadn’t practised on Saturday and I had to change a player, and that was the most rational decision.”
Arsenal have now failed to beat Chelsea in nine Premier League games, but Wenger believes his side may well have ended the wretched run had they kept 11 men on the field.
“We are frustrated because we couldn’t play the game with our real assets, and that is frustrating,” he said. “The emotional damage is of course there, because the disappointment is there, but what is important is the points we lost.
“We came out with a lot of regrets because we couldn’t play with ‘our’ team, and there was a lot of room, looking at Chelsea today, to beat them if we’d had 11 players.”
On the decision to send off Mertesacker, Wenger described Costa as “clever” having also provoked Gabriel into being sent off in the clash between the two sides earlier in the season.
“I think the red card was quick and harsh but I have to watch it again,” Wenger said of Mark Clattenburg’s decision. “Costa has got two players sent off in two games against our side. Those are only facts. So he’s clever.
“Is the decision right or wrong? I don’t know. But I said Costa got two of our players sent off in the last two games against Chelsea and that’s a fact, without accusing him of anything.
“It was frustrating, of course, but it’s a decision we had to take on the chin and get on with our job. We did that. The team were focused and resilient, fighting to the last.
“Despite the disappointing result we should have given more belief to our game by that performance.”