It was a game that Spurs dare not lose after Chelsea closed the gap on fourth place to two points over the weekend, but in truth, the home side barely broke sweat.
Watford gifted Mauricio Pochettino's men the lead on 16 minutes when Orestis Karnezis fumbled Kieran Trippier's searching cross which saw Christian Eriksen swipe the ball away from the keeper and Alli gratefully gobbled up the chance.
Returning Spurs keeper Hugo Lloris made a good one-one-one save to deny Andre Gray to preserve Spurs's lead moments later.
And they made the visitors pay just after the break, when Kane tucked away Trippier's low cross after initially fulffing his lines when Heung-min Son laid the ball on a plate for him.
Kane then missed from two yards out but had very little time to react to Jan Vertonghen's header that struck the post.
The Hornets should have got back into it on 69 minutes but Richarlison made a complete hash of Troy Deeney's knock-down as Spurs ended up coasting to victory.
The win sees Spurs go five points clear of Chelsea, while they are just one point off third place Liverpool with a game in hand.
There were a few candidates for this prize. Eriksen was pulling the strings as he has done so many times this season and Kane looked as dangerous as ever.
But the star man tonight is Kieran Trippier. Everything went through the right-back, who found a lot of joy going forward and he also looked very assured defending too.
Trippier provided Spurs' top scorer with an easy finish to effectively seal the win but it was also the right-back's awkward cross which Karnezis struggled to deal with which eventually led to Spurs taking the lead.
MOMENT OF THE MATCH
Although Spurs performed well in the game, their performance hardly set the place alight, so the moment of the match has to be Kane's miss from two yards.
Kane may have missed an open goal but he had next to no time to react to the ball that rebounded off the post.
Nevertheless, someone of Kane's outstanding scoring prowess will undoubtedly get some friendly banter about that miss!
WHAT THE MANAGERS ARE SAYING
Mauricio Pochettino was pleased with the result but admitted his side can perform better.
He said: "It is a good night for us. It is three points for us that leaves us in a good position.
"Maybe we are not playing the way we are wanting to play but it is difficult to keep playing good football.
"We tried, but Watford are difficult opponents. They played well, they created some chances."
Meanwhile, Javi Gracia bemoaned the Hornets' cheap play in their own box which helped Spurs score the goals.
He said: "We are competing, we had good performances in the last few games, but it is not enough to get points.
"We conceded cheaply in our box, we weren't able to score goals in the other box, and if you don't have control in the boxes it is difficult to win games.
WHAT THE FANS ARE SAYING
Tottenham: Lloris, Trippier, Sanchez, Vertonghen, Davies, Dier, Dembele (Wanyama 62), Eriksen, Alli (Lamela 82), Son (Sissoko 74), Kane
Subs not used: Alderweireld, Vorm, Aurier, Lucas Moura
Watford: Karnezis, Cathcart, Kabasele, Mariappa, Holebas, Capoue, Doucoure, Femenia (Deulofeu 63), Hughes (Carillo 83), Richarlison, Gray (Deeney 63)
Subs not used: Gomes, Janmaat, Britos, Sinclair
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