If Watford were not the better side in the first half than they at least created the better chances, with Etienne Capoue releasing Andre Gray on 26 minutes for a toe-poke which brought a strong save from Lloris.
Will Hughes and Abdoulaye Doucoure combined nicely 10 minutes later to fashion another opportunity which the latter worked back onto his right foot and hit powerfully, albeit straight at Lloris from 12 yards out.
Tottenham's captain has been at fault for several goals in recent weeks, but had to make his third good save of the half when he pushed away a low shot from Richarlison which was heading for the bottom corner.
The half-time anxiety around Wembley disappeared three minutes after the restart when Kane turned home Trippier's cutback, having lost his footing when trying to connect with Son Heung-min's initial cross.
Kane would have moved to within three of Liverpool's Mohamed Salah in the race for the Premier League's Golden Boot had he been able to sort his feet out to convert a close-range rebound, after Jan Vertonghen's 68th-minute header came back off the post.
Rather than a late Spurs flourish, Watford responded as well as they did in the first half and should have pulled one back when Troy Deeney knocked the ball down for Richarlison who blazed over from eight yards.
Deeney and Gerard Deulofeu had a big impact off the visiting bench and the Spaniard had a 72nd-minute goal disallowed when he was flagged for a marginal offside, before rounding Lloris and slotting into the net.
Tottenham had their own goal chalked out two minutes later when skilful build-up play from Vertonghen went to waste by Kane straying offside. The England striker would not get another bite at a second goal but he did set up Moussa Sissoko for a 90th-minute chance that the Frenchman hit over the crossbar.
Lloris was still needed to preserve a deserved clean sheet in stoppage time by keeping out Andre Carrillo on a night when Spurs were not at their best, but had enough to beat a Watford side who are over 10 hours without an away goal in the Premier League.
SPURS (4-2-3-1): Lloris; Trippier, Sanchez, Vertonghen, Davies; Dier, Dembele (Wanyama, 63'); Eriksen, Dele (Lamela, 82'), Son (Sissoko, 74'); Kane
WATFORD (4-2-3-1): Karnezis; Mariappa, Cathcart, Kabasele, Holebas; Doucoure, Capoue; Femenia (Deulofeu, 64'), Hughes (Carrillo, 83'), Richarlison; Gray (Deeney, 64')