The Hornets looked to have shut Spurs out with a strong defensive display, but the defender came up from the back in stoppage time to nod the visitors into the lead, with a medical emergency in the stands once again causing play to be temporarily halted.
Claudio Ranieri’s team was in a better position than it was on Tuesday for the 4-1 defeat against West Ham United, with William Troost-Ekong, Tom Cleverley and Jeremy Ngakia back at his disposal.
The latter pair were included among the substitutes while Troost-Ekong was brought into the defence with Kiko Femenia ruled out with a hamstring injury.
Ken Sema also came into the starting XI in place of Cucho Hernandez, while Imran Louza was brought back in to replace Ozan Tufan.
Ahead of the match, there was optimism among the Watford fan base following the news that top scorer Emmanuel Dennis would not be travelling to the African Cup of Nations this month. He gave the supporters further cause to feel positive in the second minute of the match when he created room for a shot in the penalty area after latching onto Joshua King’s threaded pass. However his effort was tame and failed to trouble Huge Lloris.
Spurs then began to dominate play but defensively, the Hornets put as many men as they could behind the ball at all times and it served a purpose, with the visitors struggling to find a route to goal.
Their first half chance came after the quarter-of-an-hour mark when Pierre Emile Hojbjerg volleyed over the bar after Craig Cathcart had headed away Emerson Royal’s delivery from the flank.
They created another glimpse of goal shortly after when Harry Kane outmuscled Imran Louza on the corner of the 18-yard box, but the England striker’s effort was straight at Daniel Bachmann, who caught under little duress.
While the home side were defending well enough and preventing the likes of Kane and Heung-Min Son from creating too much, going forward there was little to get excited about. Sema’s shot in the 25th minute was similarly uninspiring, with Lloris simply having to crouch to keep it out.
His opposite number needed a far greater display of acrobatics to deny Sergio Reguilon a moment after, when Hojbjerg rolled the ball invitingly into the path of the full-back on the edge of the box.
His left-footed strike seemed destined for the far corner, but Bachmann saved with his fingertips away to his left.
For all of Watford’s solid defensive work, cracks were beginning to show and the next chance of the match came from a mistake at the back, a problem they have encountered far too regularly this season.
This time it was Bachmann at fault, with his sloppy pass out to Louza easily picked off by Oliver Skipp. The loose pass was flicked into the path of Kane, but he guided his effort wide of the far post, under very little pressure from the recovering defenders.
Hojbjerg was picked out in the centre of the box with three minutes of the first half remaining but couldn’t make any meaningful contact with the ball and the visitors’ frustrations continued until the half time whistle.
Watford’s focus on shutting out Tottenham had come at the cost of any real attacking threat and that didn’t look like changing after the break, especially with Joao Pedro having to step onto the pitch to replace Dennis.
There was little surprise that the first chance of the second half went Spurs’ way, although it was an effort once again struck with hope rather than belief, with the Hornets creating plenty of obstacles for their guests.
Reguilon lashed into the side netting on a tight angle after Son had been unable to escape from the maze of yellow shirts in the box.
Lucas and Kane then both crafted space for shots from outside the box, as Tottenham looked to avoid the defenders that had thwarted them up to this point, but Bachmann was able to keep both efforts out.
At the other end, Lloris had to be alert to deny King, who curled towards the far corner from the edge of the box following some tenacious battling from Pedro. The Frenchman kept the effort out to his left at full stretch.
This looked to have been the catalyst Watford needed to push further up the pitch, away from their own 18-yard box, with King getting a half chance shortly after, on the end of a Louza corner.
The Hornets continued to look more aggressive going forward and might have carved an opening through Pedro after smothering yet another Spurs attack at the back.
The Brazilian’s run from halfway took him to the edge of the Spurs box, where he was unceremoniously dragged back by Skipp, leading to referee Rob Jones blowing his whistle for the free kick.
Pedro had clearly wanted to continue and play the advantage, with a one-on-one opportunity seemingly on the cards, but instead he had to try his luck from the free kick, which he blazed high into the Rookery End.
A Son backheel on the end of a drilled Royal cross reminded the home side that they would have further defensive work to do before they could relax. The Korean also forced a fine save from Bachmann on the end of a floated ball into the box from Moura, after he had peeled away from Francisco Sierralta.
Watford felt they should have had a penalty in the 81st minute when Pedro was brought down in the box by Lloris on the end of a neat through ball from King, but the keeper got the slighest of touches on the ball when making the challenge and the appeals were waved away.
Team medics were called over to the Lower Graham Taylor stand in the 85th minute to deal with a medical emergency, with scenes reminiscent of the Chelsea match earlier this season.
However, club medics were happy that the situation was under control shortly after and play resumed, with eight minutes added on at the end of the match.
That gave the visitors enough time to take a decisive lead through Sanchez’s header on the end of a Son free kick, rendering Watford’s hard work all but meaningless ahead of the break for the FA Cup.