Goals from Dele Alli and Harry Kane were enough to secure all three points for Spurs, but they had Hugo Lloris to thank as the 'keeper made vital saves - with both Richarlison and Andre Gray forcing good stops from the 31-year-old.
Spurs did get their early goal due to a mistake from the Watford 'keeper, though. Kieran Trippier's simple cross resulted in Karnezis spilling the ball, and Christian Eriksen played the ball across goal into Dele Alli - who calmly slotted home into an empty net to put the hosts 1-0 up.
Despite initially not creating much, Watford had a chance to equalise from out of nowhere when Etienne Capoue intercepted a loose ball and played in Gray, though his shot was denied by Lloris.
Lloris was called upon again when a Watford counter-attack saw Gray slot Richarlison through one-on-one, but once again the French 'keeper kept Javi Garcia's side at bay as the visitors looked to peg back Spurs.
After withstanding pressure from Watford, Spurs were looking to grab another goal to kill the game off and early in the second-half, they doubled their advantage. Kane initially slipped when Alli slotted the ball into him, but once again Kieran Trippier caused Watford's defence problems and crossed the ball back into Kane, who made no mistake from close-range to bag his 27th goal of the season.
Chances were starting to dry up, but an Eriksen free-kick found Jan Vertonghen - who's header cannoned off the post - and Kane couldn't sort his feet out quick enough to tuck into the empty net.
Richarlison should've made Spurs pay for the missed opportunity when Troy Deeney's header went into the path of the 20-year-old, however, he ballooned his shot well over the bar from close range, and the hosts were let off the hook.
It should've been 3-0 when Kane sent through Moussa Sissoko, but he was unable to convert the golden opportunity as his shot went way over the bar.
A late chance presented itself for Watford, but failing to take their chances was the story of their night as Andre Carrillo was the latest Watford player to have his shot saved by Lloris.
The result leaves Spurs five points ahead of fifth-placed Chelsea with only three games left in the season. While visitors Watford will be thankful for their early season form as the loss means they haven't won in their last ten games with their last win dating back to early February.
| #watfordfc XI v @SpursOfficial | Karnezis (GK); Mariappa (C), Cathcart, Kabasele, Holebas; Doucouré, Capoue; Femenía, Hughes, Richarlison; Gray.— Watford Football Club (@WatfordFC) April 30, 2018
Subs | Gomes (GK), Britos, Janmaat, Carrillo, Deulofeu, Sinclair, Deeney. pic.twitter.com/1EKVgR1IXO