Petr Cech suffered a nightmare Premier League debut for Arsenal as the goalkeeper's costly blunder condemned the Gunners to a shock 2-0 defeat against West Ham on Sunday. (Swansea Thwart 10-Man Chelsea)
Cech's £10 million ($15.5 million, 14.1 million euros) arrival from champions Chelsea was hailed in some quarters as the move that would tip the balance of power in the title race firmly in Arsenal's favour.
But the 33-year-old Czech was badly at fault when Senegal midfielder Cheikhou Kouyate headed West Ham into the lead late in the first half at the Emirates stadium.(Manchester United Squeeze Through)
Cech wasn't helped by an alarmingly careless display from his new team-mates, who crumbled again when Alex Oxlade-Chamberlain's mistake allowed Argentine forward Mauro Zarate to seal the most stunning result of the Premier League's opening weekend.
All the optimism surrounding Arsenal in the aftermath of last season's FA Cup final rout of Aston Villa and last weekend's Community Shield victory over Chelsea was washed away in a catastrophic start to Arsene Wenger's 20th season in charge.
The Gunners boss must have been horrified with the way his team, tipped to finally end the club's 12-year wait to win the title, were bullied by West Ham, who ended a run of 10 successive defeats against Arsenal with their first win over their London rivals since April 2007.
It was a dream start for new West Ham manager Slaven Bilic, who replaced Sam Allardyce in the close-season, and the perfect response to criticism of his decision to field a weakened team in their Europa League defeat against Astra Giurgiu on Thursday.
While Bilic celebrated with his club's supporters at full-time, Wenger wore a frown as he trudged down the tunnel, possibly to reconsider his decision to distance himself from a bid for Real Madrid striker Karim Benzema.
With French forward Olivier Giroud failing to repay Wenger's faith after being handed a start ahead of Theo Walcott, Arsenal were mostly impotent in front of goal.
Oxlade-Chamberlain popped up in space to lash a dipping volley just wide in the early stages.
The Arsenal winger then made an incisive burst down the right flank that took him past three defenders before a lofted cross picked out Santi Cazorla, who guided his volley onto the roof of the net.
- Fragile -
Aaron Ramsey came close to breaking the deadlock when the Arsenal midfielder's drive hit Aaron Cresswell and deflected onto the crossbar.
But Wenger's men weren't quite as dominant as the possession statistics suggested and West Ham debutant Dimitri Payet cleverly worked space for a long-range effort that deflected just over.
That was a warning to Arsenal's notoriously fragile defence that they couldn't afford to relax, but they were breached two minutes before half-time in the careless manner that suggested Cech's arrival is yet to spread the increased assurance he was expected to provide.
When Payet whipped a dangerous inswinging free-kick into the penalty area, Cech made the wrong choice, rushing off his line to attempt a leaping punch that got nowhere near the ball and Kouyate, left free by Laurent Koscielny's sloppy marking, gleefully punished the mistake by heading into the unguarded net.
Desperately needing an immediate response after the interval, Arsenal tried to raise their tempo and Giroud sent a shot crashing into the side-netting.
But Giroud wasted another chance, this time failing to find the power to beat Hammers goalkeeper Adrian, and in the 57th minute more lackadaisical defending allowed West Ham to double their lead.
This time Oxlade-Chamberlain was the guilty party, surrendering possession to Zarate, who turned under no pressure and hit a low strike that wasn't especially powerful but still beat Cech.
Wenger sent on Walcott and Alexis Sanchez and Arsenal laid seige to Adrian's goal late on.
But West Ham, superbly marshalled by 16-year-old midfielder Reece Oxford, held firm thanks to Adrian, who turned away efforts from Cazorla and Mesut Ozil to leave the hosts stunned.