Arsenal began their new Premier League season with a shock 2-0 defeat by West Ham after a nightmare league debut for new goal-keeper Petr Cech at Emirates Stadium.
Cheikhou Kouyate headed West Ham into the lead just two minutes before the break after poor judgment by the former Chelsea 'keeper, who was then wrong-footed by Mauro Zarate's shot in the 57th minute.
Tipped to be title challengers this season and coming off a 1-0 win over Chelsea in the Community Shield, Arsenal failed to create clear chances against a well-organised West Ham defence under new manager Slaven Bilic.
Widely seen as one of the best moves of the pre-season transfer market so far, Cech's arrival for a reported fee of about $17.3m was designed to strengthen Arsenal bid for a first league title since 2004.
However, the 33-year-old goal-keeper was caught out just before the break when Dimitri Payet sent a free kick into the area.
|Cech was left wrong-footed before conceding the second goal [Getty Images]
Cech decided to race off his line and try to clear the danger but Kouyate got to the ball first and sent a glancing header into an unguarded Arsenal net.
Arsenal fell further behind after Alex Oxlade-Chamberlain gave away possession as the home side tried to clear from the edge of its penalty area.
Zarate latched onto the ball, twisted and unleashed a low shot to Cech's right as the 'keeper prepared to cover the bigger gap to his left, sealing a result that few might have predicted.
Elsewhere, 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.
Arsenal 0-2 West Ham
Newcastle 2-2 Southampton