Arsenal spurned the opportunity to retake first place in the Premier League as they lost 2-0 to fellow Londoners West Ham United at the Emirates on Thursday.
West Ham only had three efforts on target but Tomas Soucek gave them a halftime lead before former Arsenal defender Konstantinos Mavropanos extended the advantage after the break.
– Stream on ESPN+: LaLiga, Bundesliga, more (U.S.)
Arsenal had more than twice as many chances but failed to take any as the visitors defended gamely.
West Ham took the lead against the run of play after 13 minutes when Soucek knocked home after a pull-back from Jarrod Bowen who looked as if he just managed to keep the ball in play.
After that it was an Arsenal blitz with Bukayo Saka crashing the ball against the post and Gabriel Jesus missing two good opportunities before Mavropanos scored with a thumping header from a James Ward-Prowse corner in the 55th.
West Ham could have made it three from three chances but Said Benrahma had a penalty saved in added time after a foul by former West Ham captain Declan Rice.
Second-placed Arsenal remain on 40 points, two behind Liverpool who beat Burnley 2-0 on Tuesday.