Goals from Mark De Vries and Patrick Kisnorbo sparked celebrations among the visiting fans at Vicarage Road, although they could have been spared a few anxious moments late on had Foxes converted one of a number of other good opportunities that fell their way.
After a fairly uneventful opening to the game it took the brilliance of the inspirational Dion Dublin to prevent the visitors from falling behind. Exciting Watford youngster Ashley Young looked odds on to score after speeding clear of Nils-Eric Johansson and rounding keeper Rab Douglas and rolled the ball towards the empty net, only for the vastly experienced Leicester centre-half to appear seemingly from nowhere and clear off the line.
However, Watford were made to pay the price for not taking that chance less than 60 seconds later when Momo Sylla's cross from the right was glanced across the face of goal by Stephen Hughes for De Vries to slide the ball inside Ben Foster's near post from a tight angle.
Leicester could have extended their advantage soon after when De Vries inexplicably opted to head back across goal, rather than at the target, after being found unmarked by Patrick McCarthy's long diagonal ball.
The Hornets upped the tempo at the start of the second half and were rewarded just three minutes in when Dublin was uncharacteristically caught napping by Malky Mackay's ball forward and Young seized on the centre-half's hesitancy to convert his seventh of the season in emphatic fashion, striking a rising angled drive inside Douglas' near post.
But that was as good as it got for the Hornets and less than 60 seconds later they found themselves chasing the game again when the unmarked Kisnorbo headed home a Sylla corner.
After that the game became increasingly disrupted by a high number of stoppages but the visitors enjoyed the best of what chances were created. De Vries twice went close but the best opportunity fell to substitute Iain Hume, who broke clear of the Watford defence which saw his shot rebound clear off Foster's right-hand post.
Watford pushed centre-halfs Clarke Carlisle and Mackay forward in the closing stages in a desperate attempt to salvage something from the afternoon, but the closest they came was when Marlon King fired over from the right side of the penalty area.