Arsenal boss Arsene Wenger described defeat at West Brom as a "nightmare".
The Gunners went down 2-1 at The Hawthorns to lie behind Leicester, Manchester United and Manchester City in the Barclays Premier League.
James Morrison's volley and a Mikel Arteta own goal gave the hosts - who only managed one shot on target - victory after Olivier Giroud opened the scoring.
Wenger said: "It was a very bad afternoon for us. We had 70 per cent possession, we scored an own goal, we missed a penalty, we gave away a goal from a set-piece, that is perfect to make the afternoon a nightmare.
"We missed open-goal chances. I believe West Brom did fight with 100 per cent commitment as well and you have to give them credit for that.
"At 1-0 we had just to make sure they did not come back with an easy goal and that's where we were guilty, because apart from that I cannot fault the team who gave what they could until the last minute. We produced enough to win the game."
Source: tribalfootball.com