Tottenham left it late to strengthen their Premier League top four hopes as Davinson Sanchez's injury time header downed Watford on New Year's Day.
Although Emmanuel Dennis worked Hugo Lloris with a tame effort inside 90 seconds, Watford's game plan was immediately clear as they dropped deep into a compact 4-4-2 defensive shape.
It took Spurs a while to get moving, but they troubled Daniel Bachmann in the Watford goal on 16 minutes. A cross from the right from Emerson Royal led to a mix up in the penalty area between William Troost-Ekong and Imran Louza, but Pierre-Emile Hojbjerg's resulting effort flew over the bar.
Harry Kane stung the palms of the Watford goalkeeper shortly after, before Sergio Reguilon drew a fine stop with a rasping effort from the edge of the area.
Spurs then carved out their best chance of the half on 30 minutes. Bachmann played a loose pass into Louza in midfield and when Oliver Skipp nicked in front to feed Kane, the England captain curled his effort past the far post.
The away side screamed for a penalty shortly before half time when Eric Dier went down in the penalty box under the attentions of Juraj Kucka, but the referee waved the defender's appeals away.
Spurs emerged from the interval on the front foot, and Lucas Moura tested Bachmann with a shot from distance.
The Watford goalkeeper was then forced to turn Kane's left-footed effort over the bar after the forward had swivelled past Sierralta on the edge of the penalty box.
However, Watford started to establish an attacking intent, and they went close in the 53rd minute when Hugo Lloris tipped Josh King's rasping effort round the post.
Antonio Conte's side continued to push in search of a breakthrough, and they were inches away with Royal flashed an effort across goal and Son was marginally late to react to divert the ball goalwards.
The South Korean then produced Spurs' best chance of the afternoon with a little under 20 minutes to play. Lucas clipped a delightful pass into the forward's path and Bachmann was forced into heroics to deny his volleyed effort.
The Hornets could have nicked it with ten minutes remaining when Joao Pedro went down inside the penalty area after knocking the ball past Lloris, but VAR ruled that there was no infringement from the Spurs goalkeeper.
Eight minutes of injury time were added on after a stoppage in play following a medical emergency in the crowd, and Tottenham left it until the 95th minute to deliver a gut punch to Claudio Ranieri.
Son whipped in a delcious free-kick from an angle and Sanchez flicked his header beyond Bachmann from point blank range to spark scenes of delirium in the away end.
Here's how both teams rated.
Watford player ratings
1. Goalkeeper & defenders
Daniel Bachmann (GK) - 8/10 - A few hare-brained moments trying to pass the ball into midfield, but his shot-stopping was excellent.
Craig Cathcart (RB) - 6/10 - A dependable performance and kept Son quiet when the forward drifted out to the left.
Francisco Sierralta (CB) - 7/10 - The Hornets look more assured with the Chilean at the heart of the defence.
William Troost-Ekong (CB) - 6/10 - A few clumsy moments, including a barge on Kane in the first half, but he regained his composure in the second period.
Adam Masina (LB) - 5/10 - Constantly forced infield by Lucas Moura's decoy runs.
Juraj Kucka (RM) - 7/10 - Very diligent defensive performances on the right hand side.
Moussa Sissoko (CM) - 7/10 - Helped plug the gaps in the Watford backline when the central defenders were drawn wide.
Imran Louza (CM) - 7/10 - Impressive in midfield and has surely given Ranieri food for thought going forward.
Ken Sema (LM) - 5/10 - Worked hard on the left hand side to pressurise Emerson Royal, but could do little going in the opposite direction.
Emmanuel Dennis (ST) - 3/10 - Isolated throughout and was hooked at the interval for Joao Pedro.
Josh King (ST) - 6/10 - Improved in the second half and worked Lloris with a well struck shot.
Joao Pedro (ST) - 7/10 - Added a real attacking thrust to the Hornets' performance.
Tom Cleverley (CM) - N/A
Cucho Hernandez (ST) - N/A
Tottenham player ratings
5. Goalkeeper & defenders
Hugo Lloris (GK) - 6/10 - Did well to turn King's effort round the post in the second half, but was fortunate not to concede a penalty late on.
Davinson Sanchez (CB) - 7/10 - Dealt with the Hornets' threat on the counter-attack in the second half and popped up with the late winner.
Eric Dier (CB) - 6/10 - Barely had anything to contend with, especially in the first half. Unlucky not to win a penalty.
Ben Davies (CB) - 6/10 - Really accomplished bringing the ball out of defence and switching the direction of attacks out towards Emerson Royal.
6. Wing-backs & midfielders
Emerson Royal (RWB) - 2/10 - Always spare for the diagonal switch on the right, but he did alarmingly little when the ball arrived to him.
Oliver Skipp (CM) - 7/10 - Very energetic performance, constantly snapping at the heels of Watford's midfielders to regain possession.
Pierre-Emile Hojbjerg (CM) - 5/10 - Played with the shackles on and it was a shame he wasn't allowed to burst into the final third more.
Sergio Reguilon (LWB) - 5/10 - Looked dangerous on the ball, but Spurs struggled to find him in dangerous areas. Strange decision making when he was sent through at the start of the second half.
Lucas Moura (RW) - 5/10 - Unable to stretch his legs in behind the Watford backline with so little space.
Harry Kane (ST) - 5/10 - A few nearly moments, but he was forced to do most of his work from outside of the penalty area.
Heung-min Son (LW) - 6/10 - Struggled for space to operate in with Watford encamped in their own defensive third, and was denied by a fine save from Bachmann in the second half. Ultimately did well to win and then deliver the free-kick for the winner.
Harry Winks (CM) - N/A
Giovanni Lo Celso (AM) - N/A
Bryan Gil (RW) - N/A