Kouyate gives Hammers the lead as Cech misjudges
Zarate doubles visitors lead with low shot from 20 yards
16-year-old Reece Oxford starts for West Ham
Stoke entertain Liverpool in late game
Arsenal 0-2 West Ham
Image source, Getty ImagesGood play from Diafra Sakho, who runs the ball into the corner before smacking it against Laurent Koscielny, winning the Hammers a corner.
Slaven Bilic knows this is not over yet, though, barking instructions from the edge of his technical area.
Arsenal 0-2 West Ham
Now Santi Cazorla is denied as his powerful drive is pushed away by the diving Adrian.
Some Arsenal fans have had enough, making their way to the exits, looking back briefly in disgust. It has not been a good day for the hosts.
Arsenal 0-2 West Ham
Tom, Kent: Having seen Reece Oxford in pre-season, I can see why he's started. Future England captain. You heard it here first!
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Arsenal 0-2 West Ham
Theo Walcott sees a volley blocked, before Alex Oxlade-Chamberlain sends a fierce shot into the sidenetting.
The Gunners are pressing, but time is against them.
Arsenal 0-2 West Ham
Quote MessageWest Ham have picked out a pass, they have taken care with the football and made use of it. Too often clubs have visited here and not done that. It has come from the manager Slaven Bilic saying, 'go out and express yourselves'.
Bradley Allen, Tottenham academy coach on BBC London 94.9
Image source, ReutersIt is all square in the other Premier League game as Southampton's Shane Long makes it 2-2 at Newcastle. Ten minutes to go in that one and you can keep an eye on events in our dedicated live text commentary page here.
Meanwhile, build up to Stoke v Liverpool is under way here.
Arsenal 0-2 West Ham
Youth is exchanged for experience as Reece Oxford makes way for Kevin Nolan. A very good Premier League debut for Oxford.
Arsenal 0-2 West Ham
James Baker: 14 shots and 61% possession. West Ham are a very good side but Arsenal should be winning - but no one can put it in the net.
Rhyno: This is the beauty of he Premier League. Wake up call for top four candidates.
Paul Wade: West Ham have been brilliant so far. Payet will be in everyone's dream teams now. Looks class.
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Arsenal 0-2 West Ham
Image source, Getty ImagesA break in play as Olivier Giroud and James Tomkins clash heads and both need treatment.
After a minute or two Giroud is back up on his feet. Tomkins takes a little longer, but a thumbs up from the physio to the West Ham bench suggests he is good to continue.
Arsenal 0-2 West Ham
West Ham are edging closer to a first league win at Arsenal in eight years and 16-year-old Reece Oxford has more than played his part.
The teenager has been a busy presence in the Hammers half, helping to nullify Arsenal's infrequent attacks.
Image source, Getty ImagesArsenal 0-2 West Ham
Theo Walcott races forward and shoots, deflected wide for a corner.
Once again the set piece lacks bite as the ball is sent into the area and bounces off Alexis Sanchez. The attempted clearance then hits the Chilean before West Ham clear.
Arsenal 0-2 West Ham
Nacho Monreal goes in the book for Arsenal after a foul on Mark Noble. The West Ham skipper is down injured for a lengthy spell and Arsene Wenger is not happy. He wants things hurrying up.
Arsenal 0-2 West Ham
Image source, ReutersIt is Sanchez time.
Unable to play the full 90 minutes just yet, Alexis Sanchez is introduced for the final 25, with Mathieu Debuchy making way.
Big cheer from the Arsenal fans, can he make something happen?
Arsenal 0-2 West Ham
For Arsenal, almost as bad as their defending has been their set-pieces - they have had a couple of free-kicks in promising positions but failed to make the most of them.
That's the case when Santi Cazorla sends in a free-kick from the left and Olivier Giroud meets it, but his header is straight at Adrian. Poor.
Arsenal 0-2 West Ham
Quote MessageThis is now a challenge for Slaven Bilic. What does he do? Put nine defenders on if you have to, just make sure you keep it at 2-0. What this could do for the confidence of his players will be unbelievable.
Bradley Allen, Tottenham academy coach on BBC London 94.9
Arsenal 0-2 West Ham
Scoring is Mauro Zarate's last action of the game as he makes way, somewhat reluctantly, for Matt Jarvis.
That change comes just after one for Arsenal as Theo Walcott was brought on for Francis Coquelin.
Image source, PAArsenal 0-2 West Ham
Image source, OptaIt was just far, far too easy for West Ham. Alex Oxlade-Chamberlain (15) caught out by Mauro Zarate and he fires in from outside the box.
Arsenal 0-2 West Ham
Image source, Getty ImagesK Love: Man, Arsenal NEED defenders.
David Robinson: Two West Ham goals, two Petr Cech errors.
Mark Goddard: Arsenal football club, because there can be no true despair without hope.
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Arsenal 0-2 West Ham
Quote MessageThis is the beauty of the Premier League, those coupon busting results. Arsenal didn't clear their lines and Mauro Zarate's early shot caught Petr Cech out. Did those West Ham supporters think they would be 2-0 after an hour? You are joking me. What a goal, what a performance.
Bradley Allen, Tottenham academy coach on BBC London 94.9
Arsenal 0-2 West Ham - Mauro Zarate
Image source, ReutersMy word! West Ham double their lead after shocking defending by Arsenal. Alex Oxlade-Chamberlain tries to move out of the defence with the ball but is too casual and allows Mauro Zarate to snatch possession.
The Argentine then strides towards the area before shooting low and his shot somehow creeps past Petr Cech and in at the near post.