Arsenal’s season started in defeat as West Ham won their first Premier League game under Slaven Bilic.
Keeper Petr Cech misjudged Dimitri Payet’s free-kick to allow Cheikhou Kouyate to nod in the Hammers’ first.
And after the break Mauro Zarate finished from 20 yards after being gifted the ball by the Gunners defence.
Arsenal controlled possession but were worryingly blunt in the final third, came closest when Aaron Ramsey hit the crossbar in the first half.
West Ham United capitalised on two mistakes from Arsenal’s new goalkeeper Petr Cech to claim a surprise 2-0 victory at the Emirates and bring the Gunners’ early Premier League optimism down to earth with a bump on Sunday.
Cech, signed from Premier League champions Chelsea during the close season, came flying out to punch Dimitri Payet’s free kick just before halftime but was beaten to the ball by the head of West Ham’s Cheikhou Kouyate.
Mauro Zarate doubled West Ham’s advantage in the 57th minute when his low strike beat Cech at his near post as former West Ham player Slaven Bilic enjoyed victory in his first Premier League match as a manager.
Newcastle United also have a new manager in Steve McClaren and the former England coach’s first league match in charge ended in a 2-2 draw against Southampton at St James’ Park.
Later on Sunday, Liverpool have an immediate opportunity to avenge a 6-1 loss to Stoke City on the final day of last season with a return to the Britannia Stadium.