Nicklas Bendtner's classy hat-trick booked an enticing FA Cup quarter-final at Manchester United as Arsenal swatted aside Leyton Orient.Marouane Chamakh slotted an early opener before Bendtner's superb header, then a curling finish, put Arsenal's second-string in command. Bendtner's cool third came from the penalty spot after Kieran Gibbs was tripped by Alex Revell in the box.Substitute Gael Clichy then lashed in low with 15 minutes remaining. League One Orient were routinely swept aside in this fifth-round replay, but Arsenal's crushing disappointment from Sunday's failure to collect their first trophy since 2005 - after losing the Carling Cup final to Birmingham - was hard to hide at a muted Emirates Stadium.The hosts initially looked like they lacked a spring in their step, but fears of further agony evaporated in the seventh minute with a goal of typical Arsenal quality.Irish debutant Conor Henderson - another ball-playing midfielder - probed for a gap through the back-line and the 19-year-old's deflected pass was pounced on by Tomas Rosicky, who sped to the byeline to clip a square ball through the legs of Charlie Daniels across the box.Moroccan striker Chamakh held his position to coolly side-foot the ball through the legs of Terrell Forbes from eight yards out, right into the corner of the net, for his first goal since the end of November.Orient hit back soon after as Ignasi Miquel's poor headed clearance fell for Ben Chorley.But his full-blooded volley was blocked by a crouching team-mate in front of Manuel Almunia, who nevertheless had it covered.Their best chance came when pacy Daniels twisted and turned down the left wing to whip in a dangerous low cross.Yet Revell misjudged his promising position in the area to put his point-blank snapshot wide from only six yards out.Bendtner had appeared marginally disinterested, but that changed during the course of an sparkling 20-minute spell from the Danish forward before half-time.His first goal, in the 27th-minute, was a superb effort as he leapt high to outmuscle Daniels before guiding a looping header past the reach of O's keeper Jamie Jones from a floated Gibbs cross.With that, Arsene Wenger's team took complete control.The second from Bendtner was even better that the first. Pouncing on a loose ball, he stalked into the area while teasing the ball just in front of Andrew Whing to find a gap before curling a low shot perfectly past Jones into the far corner.The hosts remained in second gear after the break although Orient, with impressive Daniels a constant outlet down the right, did at least show a sense of adventure.Abou Diaby should have added Arsenal's fourth in the 50th minute after he danced round a host of defenders on a charge towards goal.But, after a fine one-two with Chamakh set him free inside the box, he dragged his low shot just wide.It finally came in the 62nd minute when Gibbs shimmied his way into the area only to be felled by Revell, who looked uncomfortable defending.Bendtner's penalty finish was true and unerring as he completed his hat-trick before being taken off, though not before nearly gifting a goal to the east Londoners as he dallied while covering at right-back.One sour note was the withdrawal of Rosicky, who suffered concussion after a heavy collision.The 75th minute coup de grace was inevitable as injury-hit Arsenal, who host Sunderland in the Premier League before facing Barcelona away in the Champions League, pushed forward in waves.Emmanuel Eboue's testing ball across the box evaded O's defenders. Chamahk dummied and the ball just eluded substitute Jack Wilshere, but French left-back Clichy ran on to it like a stream train to propel a powerful low finish just inside the far post past overworked Jones.Source: BBC