Robin van Persie scored twice from the penalty spot as Arsenal staged a remarkable comeback to knock Aston Villa out of the FA Cup.Villa led 2-0 at the break through a Richard Dunne header and a finish from an acute angle by Darren Bent.But three goals in seven minutes turned the tie upside down, Van Persie making it 2-1 after Dunne fouled Aaron Ramsey.Theo Walcott levelled before Van Persie sealed victory with a second spotkick after Bent's foul on Laurent Koscielny.Arsenal, 10-times winners of the FA Cup, will now visit the winners of next week's Middlesbrough-Sunderland fourth-round replay.As for Villa, manager Alex McLeish will be wondering how on earth his side lost from a winning position.McLeish denied Arsenal a first trophy since 2005 11 months ago when he steered Birmingham City to a famous win over the Gunners in last season's Carling Cup final.But the Scot was the one left shell-shocked this time as Arsenal staged a magnificent fightback.The Gunners were in desperate need of a lift after losing three straight league games, and the early exchanges suggested they were determined to make amends for their recent poor form.Villa keeper Shay Given was forced into a stunning fifth minute save to keep out Thomas Vermaelen's 30-yard thunderbolt before Walcott was guilty of slicing a glorious opportunity wide.The England international skipped past a challenge after Tomas Rosicky's 13th minute pass, but Walcott lost his composure at the crucial moment.Villa had won on their last visit to the Emirates towards the end of last season but they were struggling to venture out of their own half as Alex Oxlade-Chamberlain flashed another chance wide.However, McLeish's side weathered the early storm before taking a firm grip with two goals in 12 minutes before half-time.The visitors looked dangerous on the break through Bent and Robbie Keane, but it was a set-piece that undid the Gunners as Dunne broke the deadlock with a goal made in Dublin.A well-worked corner saw Stiliyan Petrov's backheel release Keane, who floated the ball to Republic of Ireland team-mate Dunne, who headed home from close range.It went from bad to worse for Arsenal when Bent then finished from an acute angle after his initial shot had been beaten away.Villa's 5,000-strong travelling fans were in dreamland, but it was not to last.Dunne, who had already been booked, was lucky to remain on the pitch after hauling down Ramsey inside the area, Van Persie making no mistake from the spot in the 54th minute.And, within two minutes, Arsenal were level.Walcott darted into the right side of the Villa penalty area and stabbed the ball across the goal-line, where Alan Hutton smashed his clearance back against the England forward and it ricocheted into the net.Then, in the 61st minute, it was 3-2 after another well-executed finish by Van Persie from the penalty spot after Bent sent Koscielny sprawling.And there was no coming back for stunned Villa as the Emirates celebrated one of the most dramatic victories in their six seasons at the venue.