Son Heung-Min opened the scoring for the home side three minutes before half time and there will be added joy when Spurs fans look at the table, with their team at the summit and bitter rivals Arsenal rock bottom.
Kane this week said he will remain at Tottenham this summer, despite Manchester City's summer-long attempts to prise him away, and after he made a scoring return to action in midweek in the club's Europa Conference League win, he was in from the start here.
Tottenham boss Nuno Espirito Santo made one change from the win over Wolves last time out in the league, with Kane coming in for Lucas Moura, and the striker was met with a wall of cheers as he led his team out for the match. Watford, meanwhile, named Moussa Sissoko in their starting XI, two days after his departure from Spurs.
Sissoko was in the thick of the action inside the first minute as he found Juraj Kucka but his shot was headed off the line by Eric Dier in a dramatic start to the game which began with Kane wanting a penalty after 30 seconds when he was bundled over in the box.
Tottenham woke up, though, and gradually took control of the game, as Watford stood firm in the early stages to repel wave after wave of attacks from Nuno's men.
Watford thought they had done enough to go in level at the break but Son's fortunate free kick evaded everyone and ended in the back of the net. Son whipped in a dangerous ball but no Tottenham touch was forthcoming, and it flew all the way in to hand Spurs the lead.
Dele Alli squandered a great chance to put Tottenham further ahead when he screwed wide from close range with a quarter of the game to go, but it did not matter as Nuno's men claimed the win.
"Sonny is fantastic but I still think he has a long way to go. He will improve his numbers alongside the team. He is a fantastic team player, the way he works. I am happy for him, but the challenge is to push further," Nuno BEIN Sports.
"The players worked hard for that win. In order to achieve consistency, it will take time. It was a difficult game, but really good movement in the second half. There were chances that we have to be more clinical with."