It was the South Korean’s 200th Premier League appearance and his 72nd goal. Not that he meant it of course.
His intention was always to whip the ball in from the far left, but it dipped and curled and, after a wicked bounce, nestled in the far corner.
It was no less that Tottenham deserved for their dominance but they could still count themselves lucky having offered little threat to the goal.
Harry Kane’s first start of the season following his summer-long flirtation with Manchester City carried the promise of a goal but Tottenham couldn’t find him.
Dele Alli and Pierre-Emile Hojbjerg commanded the midfield, with Steven Bergwijn offering width, but the movement was a combination ponderous and predictable. After 20 minutes Watford retreated 15 yards and were content to pick their moment to break.
Tottenham fullback Japhet Tanganga had a commendable game but manager Nuno Espirito Santo will want to see him hug the touchline with greater regularity. When he did hang out wide he was able to stretch the Watford back four and cut inside to the space that he had helped create.
The free kick that led to Son’s goal was a result of Tottenham stretching the play from flank to flank and will give the manager food for thought as he packs up his tools ahead of the international break.
The second half saw Watford come out of their shell and resulted in a better spectacle. Tottenham old boy Moussa Sissoko - who received a friendly reception from the home crowd - will rue his missed chance that sailed high and wide from the edge of the box.
Kane came close twice within a minute. First he failed to connect with a Lucas Moura cross around his ankles and then saw his sweetly struck volley well saved by Daniel Bachmann.
It wasn’t a classic, but Tottenham sit pretty at the summit of the table and have now won their first three games without conceding a goal for the first time in their history.