Jonathan Tehoue's stunning 89th minute equaliser earned League One side Leyton Orient an unlikely FA Cup fifth round replay with Arsenal.
The Gunners had dominated possession for most of the tie and thought Tomas Rosicky's second-half header would be enough to set up a quarter-final clash with Manchester United.
But Orient, who came into the match on the back of an incredible run of only one defeat in their last 20 games, never gave up and got their reward when substitute Tehoue bulldozed his way through two challenges and buried his shot past Manuel Almunia.
It had already been a frustrating day for the Gunners, who came to Brisbane Road on the back of their midweek Champions League win over Barcelona looking to maintain their push for silverware on four fronts.
This game was always going to be a very different test to the clash with the Spaniards, especially since Gunners boss Arsene Wenger picked a very different team, making 10 changes.
Alex Song was the only survivor of that victory in the starting XI at Brisbane Road but a side containing Rosicky, Andrey Arshavin and Marouane Chamakh should still have seen off Orient with ease.
But they did not, mainly because of a lack of urgency in the final third, and some poor finishing when they did turn their vastly superior possession into chances.
Too often, they were kept at arms length - Nicklas Bendtner and Chamakh failed to trouble O's keeper Jamie Jones with efforts from the edge of the box and even Jones' best save - from Arshavin's snap-shot - was a relatively straightforward near-post stop.
It was not all one-way traffic, with Charlie Daniels sending a 30-yard drive fizzing over the bar from a quickly-taken corner.
But Arsenal should still have been ahead at the break when Kieran Gibbs overlapped down the left and sent in a perfect cross, only for the unmarked Chamakh to slice his shot horribly wide from near the penalty spot.
That lack of cutting edge left Wenger with plenty to ponder at the interval but in the end he did not have to wait long to see his side break the deadlock.
The Gunners continued to attack and finally got their reward in the 52nd minute, when Rosicky met Bendtner's cross with a neat header that nestled into the bottom corner of the net.
That still left Orient more than half-an-hour to find an equaliser, however, and they threatened an instant response when Alex Revell met Dean Cox's cross, but saw his looping header easily saved.
Arsenal appeared the more likely to score a second, with only a fine double save by Jones denying Rosicky from Arshavin's pull-back.
But while there was only one goal in it, Orient remained hopeful and they continued to press forward.
Revell had fired wide with a sweeping shot before the home side had appeals for a penalty turned down when the striker's effort hit Sebastien Squillaci in the face.
It appeared the O's final chance had come and gone before Tehoue surged forward, but his powerful finish means the east Londoners have a lucrative replay to look forward to on top of the £800,000 they have already made from this Cup run.
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