Arsenal threw away the chance of a fifth straight Barclays Premier League win as West Ham battled back to earn a 2-2 draw at Upton Park.
The Gunners had looked in complete control following first-half goals from Robin van Persie and William Gallas.
However, Carlton Cole pulled a goal back before substitute Alessandro Diamanti netted a late penalty.
West Ham finished with 10 men when Scott Parker was shown a second yellow card, but were not to be denied a much-needed positive result.
Gianfranco Zola's men had shown plenty of early promise, when Cole's drive was charged down before again being undone by some poor defending.
Arsenal slowly started to get themselves on top, with Robert Green standing up well at the near post to palm Van Persie's angled drive behind for a corner.
At the other end, Vito Mannone - again preferred in goal to Manuel Almunia - needed treatment after being clattered by James Tomkins when coming to collect a corner.
Arsenal felt they had a strong shout for a penalty when, on 11 minutes, Van Persie's strike appeared to hit Matthew Upson, the former Gunners defender, on the arm, but referee Chris Foy thought otherwise.
Eventually, though, the visitors took the lead on 16 minutes.
Abou Diaby fed full-back Bacary Sagna on the overlap down the right.
The French defender whipped the ball across the six-yard box, where Green came to palm it away, only to collide with Tomkins, leaving Van Persie free to slot into an empty net for his sixth goal of the season.
Despite the setback, West Ham remained positive.
Cole continued to ask questions of the Arsenal defence, with Gallas getting across to clear after another powerful run down the right.
Arsenal, though, weathered the period of West Ham pressure, and slowly took charge of midfield again.
Upton Park was subdued, with the home fans starting to get restless before Arsenal doubled their lead on 37 minutes.
A 25-yard shot from Cesc Fabregas was deflected behind for a corner.
Van Persie whipped the ball across towards the far post, where Gallas got up to thump a header past Parker on the line.
In stoppage time, Green, hoping to be part of England's World Cup squad, got down quickly to save well from Emmanuel Eboue's low, angled drive.
West Ham had more impetus about them following the restart.
Alexandre Song fouled Cole to concede a free-kick 30 yards out, just left of centre.
The delivery from Mark Noble, though, was poor and the move eventually broke down.
Andrey Arshavin, who up until now had been largely anonymous, dashed into the left side of the West Ham area, before drilling a low ball across the face of goal.
Italian Diamanti, sent on just before the hour mark, at least injected some life into the West Ham attack, as he fired a 35-yard effort wide.
Cesc Fabregas then almost drilled in a third from a shorter distance, but the ball flew just wide of the top right corner.
England Under-21 youngster Zavon Hines, also on as a substitute, knocked the ball down to Cole, who turned and fired just wide.
This was a good spell for the Hammers, as Clichy made an important block when Hinds looked to get away his shot from eight yards.
Fabregas broke quickly, before feeding Arshavin and Green was at full stretch to beat away the Russian's 20-yard effort.
Diaby then wrestled Hinds to the ground, giving away a needless free-kick in a dangerous position, five yards outside the area on the left.
Diamanti smashed the ball goalwards, which Mannone did well to keep out, but pushed it back to the six-yard box where Cole headed in to give West Ham a life-line on 74 minutes.
The home fans were screaming for a penalty when Parker went down after running into Gallas, but the referee waved play on.
However, a spot-kick was given with 10 minutes left when Song tripped Cole.
After Mannone had been booked for not going back on his line, Diamanti levelled to send Upton Park into delirium.
West Ham were reduced to 10 men when Parker, already booked, was shown a second yellow card for deliberately falling on the ball as Fabregas charged clear.
Diaby was substituted for Eduardo as Wenger went for the win.
However, the Hammers were not to be denied during four minutes of stoppage time, when Green somehow kept out van Persie's header.
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