Our top-four hopes have suffered a sizeable setback thanks to Declan Rice’s first-ever goal for West Ham.
The teenager fired Samir Nasri’s pass beyond Bernd Leno early in the second half and, despite plenty of possession and chances, we couldn’t find an equaliser.
We started this London derby on the front foot, conjuring up five shots in the first 15 minutes with Alex Lacazette especially to the fore.
But the shots dried up for us and West Ham edged their way into the game. Indeed, only last-ditch interventions from Laurent Koscielny and Sokratis kept them at bay.
Former Gunner Nasri - making his Premier League debut for the Hammers - was an increasing influence, and he set up Felipe Anderson for a shot that fizzed just wide.
We needed to regroup and half-time gave us that opportunity, but it was West Ham who started the second half on top.
We invited pressure, in fairness, giving away a free-kick and then a corner. And it was from the latter that West Ham eventually took the lead after a poor defensive header allowed Nasri to pick out Rice for a first-time finish.
Unai Emery brought on Lucas Torreira and Aaron Ramsey in an attempt to turn the tide, and there were certainly gaps in the West Ham defence to exploit.
A ricochet nearly did the trick, Lukasz Fabianski just getting back to grab the ball before it crossed the line.
Pierre-Emerick Aubameyang missed a good chance after collecting a low pass from Sead Kolasinac.
And Alex Iwobi shot just wide after a delightful flick from Ramsey.
But that was as close as we got.
HOW IT HAPPENED
WHAT IT MEANS
This result keeps us in fifth place, three points behind Chelsea and three points ahead of Manchester United.
Both of those sides were due to play later in the weekend.
We were unchanged from the side that started our last Premier League game against Fulham - but there were a couple of tweaks to the squad.
Hector Bellerin and Nacho Monreal, back in full training after injury, were among the substitutes.
Lucas Torreira was also on the bench, but there was no place for Mesut Ozil in the squad.
We’ve got a huge Premier League game next Saturday, against Chelsea at Emirates Stadium.
That’s followed by another big one at home - Manchester United in the Emirates FA Cup.
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