Gary Hooper's midas touch and Josh Murphy's stunning debut goal sealed a breathless Capital One Cup third round comeback for Norwich City at Vicarage Road on Tuesday night.

Chris Hughton's men looked to be slipping meekly out of the competition after Javier Acuna and Davide Faraoni had fired Watford into a commanding lead.

City's plight called for desperate measures but even Hughton could not have predicted Murphy's pivotal impact. The academy starlet's 77th minute thunderbolt reduced the arrears before Hooper rose imperiously at the near post in the final seconds of normal time to glance home an equaliser from Nathan Redmond's cross.

Norwich visibly grew in stature and it was fitting the predatory Hooper should race through onto Leroy Fer's ball to slot between Jonathan Bond's legs in the 115th minute to clinch a place in the last 16.

City had controlled the opening period with Wes Hoolahan prominent in a chief support role to Hooper as one of eight changes from the weekend Premier League defeat to Aston Villa. But it was Watford who made the most of a rare incursion into enemy territory to open the scoring when Acuna rolled Ryan Bennett to thump past Mark Bunn from the edge of the visiting area.

Hughton emerged at the front of his technical area imploring the Canaries' backline to squeeze higher up the pitch in a bid to swiftly re-gain their midfield control. Hooper's cute reverse ball freed Hoolahan but the Republic of Ireland international was crowded out at the concession of a corner, which Steven Whittaker glanced wide at the near post. Josh McEachran's Watford debut came to an abrupt halt five minutes before the interval after the on-loan Chelsea starlet failed to recover from an awkward tumble.

Hoolahan remained the dominant operator in that congested midfield and Bond went full length to tip over his 25 yarder before Bradley Johnson came even closer when his powerful header barely six yards out cannoned against Bond's bar and back into play. City's urgency almost proved their undoing in the final minute of the opening period when Russell Martin's wayward header with Watford penned deep inside their own penalty area helped the Hornets' trigger a rapier counter, only for Acuna's long range strike to lack the precision of his earlier goal.

Johan Elmander replaced Javier Garrido at the interval, pushing Martin Olsson back into the defensive berth vacated by the Spaniard and Redmond switching to the left. Bunn was forced to make a double stop straight after the restart to deny the lively Faraoni twice with City looking sluggish in their collective efforts. Bunn then denied the newly-introduced Troy Deeney at his near post after Diego Fabbrini had skipped past Martin, but the over-worked City keeper had no chance with Faraoni's long range howitzer that flew into his top right-hand corner from 25 yards in the 55th minute to double the Hornets' lead.

City continued to exhibit distress signals in the immediate aftermath of slipping further behind, with only Bennett's last ditch sliding block denying Deeney. Hughton turned to one of the club's brightest young talents to try and turn the tide with Murphy introduced for his senior debut in place of Johnson, but Bunn was again required to claim Cristian Battocchio's free-kick.

City needed a spark and it was Murphy who provided it with a hammer strike from 25 yards the equal of Faraoni's goal after Redmond cut inside off the right flank to tee up his fellow teenager. Norwich poured forward with the away support now in full voice but Fer's towering header dropped wide. Bond then clawed out Fer's looping right-footer with Watford starting to buckle under the onslaught before Watford's keeper flapped at Redmond's corner, but Martin's header was scrambled away.

City were rewarded for their persistence when they surged forward again with seconds left in the five minutes of additional time and Redmond's cross was glanced home by Hooper at the near post to spark wild scenes of celebration in front of the away end. Referee Martin's full-time whistle blew before the sides could even restart to underline how close Hughton's men had come to a cup exit in normal time.

Bunn dropped on Deeney's miscued strike five minutes into an opening extra-time period that was to prove an antidote to the excitement of City's late fireworks. Martin glanced a header over before Watford scrambled Bennett's far post flick away with Norwich re-establishing the impressive level of their early territorial hegemony.

Redmond now looked capable of terrorising Marco Cassetti at will down the right and, not to be outdone, Murphy dived inside two Watford defenders but his driven cross evaded Hooper at the far post. City's new predator made no mistake when he raced through unopposed in the 115th minute to calmly draw Bond and drill between the keeper's legs. There was still time for Bunn to deny Deeney with a wonderful fingertip save before City could secure their place in the next round.

• Watford: Bond, Belkalem, Ekstrand, Battocchio, McEachran (Smith 39), Acuna (Deeney 52), Murray, Pudil, Faraoni, Fabbrini (Forestieri 86), Cassetti. Subs (not used): Woods, Brown, McGugan, Anya.

• Bookings: Smith (foul on Bennett, 74), Deeney (foul on Elmander, 118), Pudil (foul on Bunn, 120).

Goals: Acuna (23), Faraoni (55)

• Norwich: Bunn, Whittaker, Martin, Bennett, Garrido (Elmander 45), Redmond, Tettey, Johnson (Murphy 68), Olsson, Hoolahan (Fer 74), Hooper. Subs (not used): Nash, Turner, Howson, Becchio.

• Bookings: Tettey (foul on Fabbrini, 68), Elmander (foul on Deeney, 118), Bunn (foul on Pudil, 120).

• Goals: Murphy (77), Hooper (90+5, 115)

• Time added on: 1 minute / 5 minutes

• Referee: Stephen Martin (Staffordshire)

• Attendance: 11,178 (1,841 away)