Arsenal were unable to find a way past Blackburn goalkeeper Brad Friedel in a goalless draw at the Emirates Stadium while the Red Devils were left red-faced after a 1-1 draw with a second-string Reading side.

Chelsea, who are still in the hunt for four trophies this season, were joined in the quarter-finals by Watford, who snatched a late winner at home to Ipswich, and Plymouth, who reached the last eight for the first time since 1984 courtesy of a 2-0 win over Championship pacesetters Derby at Home Park.

West Brom twice came from behind to earn a 2-2 draw at Middlesbrough.

Icelandic midfielder Brynjar Gunnarsson was Reading's hero at Old Trafford, heading in a second-half equaliser after Michael Carrick had fired United ahead with a low 25-yarder with virtually the last kick of the first half.

United squandered a string of chances to kill off what was virtually a reserve Reading side.

Norwich lived up to their pre-match pledge to have a go at Chelsa with a lively start in which Dickson Etuhu struck the post and Lee Croft's follow-up was cleared off the line by Khalid Boulahrouz.

But the Canaries were deflated six minutes before the break when a Shaun Wright-Phillips shot was deflected past substitute goalkeeper Paul Gallagher.

Drogba's close-range volley made the outcome safe six minutes after the break and strikes by Michael Essien and Andriy Shevchenko put a flattering gloss on the scoreline.

The win was marred by a recurrence of the injury jinx that has been haunting Chelsea all season with Boulahrouz forced off with a dislocated shoulder having only just returned to action following a knee ligament injury.

Friedel earned Blackburn a replay by producing a string of top-quality saves, capped by a superb double stop in the dying seconds which saw him fling himself to his right to tip away Thierry Henry's close-range shot before scrambling to his left to block Justin Hoyte's fierce low drive.

Nigeria striker Aiyegbeni Yakubu rediscovered his touch from the penalty spot but could not prevent Middlesbrough from being held by West Brom.

Yakubu, who missed two penalties in midweek, converted from the spot on the stroke of half-time after Mark Schwarzer had allowed Diomansy Kamara's shot to trickle through his fingers to cancel out Julio Arca's early header.

Kevin Phillips grabbed West Brom's second equaliser with a deflected shot and the Baggies held on in the final stages after defender Curtis Davies was sent off after receiving a second booking for a foul on Mark Viduka.

Kevin Gallen only managed to convert one of the two first-half penalties that Plymouth won against Derby but on-loan Chelsea teenager Scott Sinclair made sure of the win for Ian Holloway's side with a late strike.

Damien Francis ensured the recent upturn in Watford's fortunes continued by scoring with a low shot after good work by Tommy Smith on the right wing, two minutes from the end of a tight battle against Ipswich at Vicarage Road.