Per Mertesacker red card for Costa foul costs Arsenal against Chelsea
Arsenal have lost twice to Chelsea this season and had a man sent off in each match. Sunday's 1-0 defeat was utterly avoidable.
Per Mertesacker had a moment of madness in the 18th minute, the German sent off for a challenge on Diego Costa, Arsenal's familiar nemesis. There was no contact with the Spanish international, but he would always take the chance to go down. From there, a team that has been struggling for Premier League form was always going to find it difficult against one as experienced as Chelsea.
Costa, the pantomime villain, provided what turned out to be the killer blow, ghosting between an Arsenal defence that hadn't quite reorganised in Mertesacker's absence to score the only goal of the game.
Arsenal should have equalised before half-time when Mathieu Flamini poked over from close range, and in the second period there was no lack of effort from the 10 men, but ultimately they couldn't find a way through.
This was a disappointing defeat and it's Arsene Wenger's job to ensure it doesn't end up being too demoralising.
Player ratings (1-10; 10=best. Players introduced after 70 minutes get no rating):
GK Petr Cech, 7 -- Had no chance with the goal and was otherwise a solid presence against his old club. When he went up for a late corner there were hopes of a Hollywood script equaliser, but it wasn't to be.
DF Hector Bellerin, 6 -- Worked really hard, defended well and tried to make things happen in the Chelsea half.
DF Per Mertesacker, 2 -- The challenge on Costa was a red card and he can have no complaints. Quite why he glanced right before sliding in is a question only he can answer. Will serve a one match ban.
DF Laurent Koscielny, 6 -- Careless early on to provide a chance for Oscar but grew into the game and ended up playing as a forward as the Gunners looked for the equaliser. Added some much-needed aggression.
DF Nacho Monreal, 6 -- The Spaniard has been one of the team's best players this season, but he might feel he could have closed down Branislav Ivanovic before his cross led to the only goal of the game. His delivery in the final third wasn't as good as normal, but he didn't really have anyone to aim for after Olivier Giroud went off.
MF Mathieu Flamini, 4 -- Had more attempts on goal than any other Arsenal player and really should have scored before half-time. He will have nightmares about that chance and rightly so. Sloppy on the ball too.
MF Aaron Ramsey, 6.5 -- On a day when Arsenal were flat, he was all energy for the duration of the 90 minutes. He tried to make things happen, won five out of seven tackles and made eight ball recoveries. Yet once more we saw evidence that the partnership with Flamini simply doesn't work.
MF Mesut Ozil, 5 -- On days like this it feels as if he's a slave to what's happening around him. Chelsea found him and his craft easy to deal with.
MF Joel Campbell, 5 -- Found it very difficult to impose himself on the game, but he'll look back on an early chance when he miskicked in front of goal with some regrets.
MF Theo Walcott, 4 -- His passing stats show he completed 18/19, but what they don't show is how many times he lost the ball, failed to control it or got knocked off it. Another poor display from a player in no form right now.
FW Olivier Giroud, N/A -- It's difficult to give him a rating as he was the man sacrificed for Gabriel after the Mertesacker dismissal. Perhaps it was because he'd picked up a knock in training this week and Wenger was being cautious, but in hindsight it looks a bad decision.
DF Gabriel, 6 -- Generally did fine, showing plenty of aggression, but being thrown in straight after the red card probably contributed to the goal Arsenal conceded, as he let Costa run off him to poke home.
MF Alexis Sanchez, 6 -- Looked rusty, as you'd expect. Added something to the 10 men who were driving for an equaliser. Sadly couldn't make an explosive return to action.
MF Alex Oxlade-Chamberlain, N/A -- Lively enough but unable to find the spark.
Andrew Mangan is one of ESPN FC's Arsenal bloggers. You can follow him on Twitter: @arseblog.