Paulo Gazzaniga dived low to his right to deny the Hornets captain following Jan Vertonghen’s handball within the last half.
Watford goalkeeper ben Foster saved from Nathaniel Chalobah and Lucas Moura before half-time to thwart Jose Mourinho’s side.
Deeney had headed a decent probability straight at Gazzaniga simply before the break, whereas Abdoulaye Doucoure shot into the side-netting early within the last half.
Watford substitute Ignacio Pussetto, creating his debut for the club, cleared AN Erik Lamela chance off the line in stoppage time at the end of the match.
The Hornets, who were at the lowest of the table when manager Nigel Pearson took over in early December, move up to sixteenth, whereas Spurs are seventh after a fourth game without a win.