Leon Best grabbed an 84th-minute winner to seal a remarkable fightback for Coventry and end Watford's seven-match unbeaten run in the Coca-Cola Championship.
The Hornets were yet to taste defeat at Vicarage Road heading into the encounter and held the second tier's longest undefeated sequence.
However, that was all brought to an end by a Sky Blues side who, in contrast, had previously recorded just two league victories on the road in 2009.
Sammy Clingan opened the scoring for the visitors with a drilled effort in the 14th minute but Watford were ahead at the interval courtesy of Tom Cleverley and Will Hoskins.
The home side wasted a host of good chances throughout and they were made to pay as Best twice found the net in the final 23 minutes to grab his fourth and fifth goals in his last five games
The hosts applied pressure straight from the off and Hornets striker Hoskins somehow diverted the ball over the crossbar from four yards after just 51 seconds.
The frantic start set the scene for an open encounter and it was no surprise when the breakthrough came with just 14 minutes on the clock.
Summer signing Clingan grabbed his second impressive goal of the season after his stunning free-kick at Preston, finding the bottom corner through a crowd of bodies from around 25 yards out.
But the lead lasted just seven minutes before Cleverley capitalised on some hesitant defending to level for Watford with a low half-volley from inside the penalty area after Don Cowie's cross was flicked on by Danny Graham.
Keiren Westwood did well to deny Graham just minutes later after a short back pass from Elliott Ward as Coventry's defence failed to settle.
The hosts started to dominate as the first half wore on, showing more steel and quality as the visitors struggled to get the grips with the clash.
And Malky Mackay's side gained the upper hand eight minutes before the interval, breaking upfield quickly after a Coventry attack was closed down.
The Sky Blues' defence was again unconvincing as they looked to deal with the counter and it was left for Hoskins to drill home after the ball broke in his direction.
Watford were in complete control as the first half drew to a close, handing Coventry a severe lesson as Westwood kept the visitors in the game with a couple of fine saves.
In similar fashion to the first half, the Hornets wasted a great chance to find the net within seconds of the restart as Graham somehow blazed over from 12 yards when in acres of space.
The home side would surely have been out of sight had they made it 3-1 but, instead, the Sky Blues enjoyed a period of dominance as the match wore on.
And they were rewarded in the 67th minute when Leon Best headed home after Ward did well to head Clingan's deep corner back across goal.
Both keepers were called into action as the game approached the final 15 minutes but it was Best who poked home at the back post six minutes from time.
Watford pressed in the final stages and some superb goalkeeping by Westwood, along with some good fortune, ensured Coventry secured their first victory over Watford in six attempts.
Teams
Watford Loach, Hodson (Oshodi 78), Mariappa, Bennett, Doyley,Cowie (Lansbury 57), Harley, Cleverley, Eustace, Graham,Hoskins (Henderson 70).
Subs Not Used: Lee, Severin, Bryan, Sordell.
Goals: Cleverley 21, Hoskins 37.
Coventry Westwood, Clarke (Cranie 69), Wright, Ward,Van Aanholt, Clingan, Gunnarsson (Osbourne 86), Cork, Best,Morrison, McIndoe (Eastwood 72).
Subs Not Used: Konstantopoulos, Walker, Cain, Jeffers.
Goals: Clingan 14, Best 67, 84.
Att: 13,034
Ref: Andre Marriner (W Midlands).
