Arsène Wenger's quest for the quadruple now means negotiating at least one more match than he had bargained for. An unwelcome replay against valiant Leyton Orient further congests Arsenal's run-in and will place additional pressure on a squad that, on the evidence of their display here, may not be as strong as their manager believes. None of which will concern Orient, of course, who fully earned a second crack at Arsenal. With a quarter-final meeting with Manchester United at Old Trafford on offer, Orient are likely to be just as determined at the Emirates.

Right from the outset here it was apparent that Arsenal would not be allowed to canter to victory. Their League One hosts passed crisply, tackled neatly and proved themselves to be as organised as they were tenacious. Arsenal, then, would have to produce at least some of the ingenuity that befits their status as Champions League contenders. However, with 10 of the players who started against Barcelona on Wednesday omitted, they struggled to do so. They circulated the ball nicely and Andrey Arshavin and Nicklas Bendtner offered intermittent evidence of rarefied skill but in general Wenger's team were predictable and one-paced. Orient did not suffer as much as they might have feared they would.

It was Orient who forged the first shot on target, their dynamic captain, Stephen Dawson, surging from midfield to test Manuel Almunia with a fierce low effort from 20 yards. The goalkeeper, making his first appearance since his outing in the last round, needed two tries to hold it.

Marouane Chamakh, who was also returning to the Arsenal team after a spell on the sidelines, was presented with a chance to put Arsenal in front moments later but headed tamely at Jamie Jones from eight yards. The Moroccan continued in that vein for the rest of the first period, his display doing nothing to suggest that he is close to recovering from the fatigue that he says has beset him in his first season in English football. He was not the only player who lacked vim, as Denílson, Alex Song and Tomas Rosicky also struggled to distinguish themselves, especially in the first half. Arshavin, however, was lively and at the hub of most of what Arsenal did well. Twice in the first period he deftly brought the overlapping Kieran Gibbs into play but the left-back's enterprise was not equalled.

The Russian forced an awkward save from Jones in the 20th minute with a swirling shot from the edge of the box following neat interplay with Bendtner. Both Arshavin and Bendtner had several more shots from similar distances in the first half but persistently failed to find the target.

Russell Slade's team did not get many opportunities to trouble an Arsenal defence in which the 18-year-old Spaniard Ignasi Miquel was making his debut, though, following a 13th-minute corner, Charlie Daniels cracked a ferocious shot just over the bar from 25 yards. Arsenal did improve in the second period, the embarrassing prospect of having to call substitutes such as Cesc Fábregas, Samir Nasri and Jack Wilshere to the rescue perhaps spurring the starters.

In the 53rd minute Bendtner and Rosicky combined finally to assert the visitors' superiority. After good work by the Dane and an inviting cross from the right, Rosicky darted from deep to nod into the net from nine yards.

Arsenal's dominance of possession increased after that but Orient did not surrender. Two minutes after going behind Daniels raided down the left and chipped a good cross to Alex Revell, who sent a looping header just over. "When they got the goal we actually came out of our shell a little and started to make one or two more passes and got a little bit of momentum," said the Orient manager.

In the 82nd minute Orient strung together their best move of the match, building intricately down the right before releasing Jonathan Téhoué, who showed composure to play a precise low ball towards Revell, the striker arriving at pace to unleash a thunderous shot from 16 yards. Almunia would have struggled to save it, so was no doubt grateful that Miquel blocked the shot with his face.

His fellow Frenchman, Wenger, admitted afterwards that he had never heard of Téhoué, who had entered the fray as a 63rd-minute substitute. One minute from time he gave the Arsenal manager something to remember him by, beating two players outside the area and rifling the ball under Almunia.

"All eight goals he has scored this season have come in the 85th-minute or later, so in terms of super-sub he's the boy!" said Slade before highlighting the feats of all his players this season. "We've only lost one of our last 21 matches, so something must be going right down at the Orient."