Tottenham substitute Son Heung-min broke Watford's hearts with an injury-time winner as Spurs snatched a 2-1 win against the 10-man Hornets.
Watford hung on for the best part of half an hour at Vicarage Road after Nathan Ake had been sent off in the second half but Son's clever finish secured a dramatic win for Pochettino's side.
Odion Ighalo had earlier cancelled out Erik Lamela's opener with his 14th goal of the season as Tottenham climb to third, above Manchester City who play on Tuesday.
Pochettino has made few changes to his side this season but Spurs lined up in an unfamiliar 3-4-2-1 with Eric Dier dropping into a back three, presumably for extra cover against Watford's deadly attacking duo Troy Deeney and Ighalo.
Heurelho Gomes and Etienne Capoue, both excellent for the Hornets this season, were up against their former club and Capoue looked keen to make a point early on, unleashing two shots from distance but shanked both, much to the delight of the Tottenham fans.
Their joy was doubled soon after as Craig Cathcart gave possession away in midfield and Lamela took full advantage, carrying the ball all the way to the Watford penalty area before coolly sliding into the bottom corner for his eighth goal of the season.
Pochettino's new system had kept the Hornets' front two quiet for most of the half but Ighalo only needs a sniff and in the 41st minute he got it, manoeuvring an awkward bouncing ball through the legs of Dier and poking an equaliser past Hugo Lloris.
Mousa Dembele, struggling ahead of the game with an ankle injury, was replaced by Christian Eriksen before half-time but Spurs stuck to their shape and looked dangerous early in the second period.
Lamela was twice allowed to run free down the right and Kane almost converted his cross but headed wide at the near post.
The visitors were on top and their charge was aided in the 62nd minute when Ake tried to win a bouncing ball but his high challenge instead caught the thigh of Lamela studs up, and referee Anthony Taylor pulled out a red card.
The next 10 minutes became something of a training ground exercise as Tottenham launched wave after wave of attack but failed to find a way through Watford's rigid defence.
For a brief moment the home side thought they had won it when a corner looked to have flown straight in but it had not crossed the line and instead it was Spurs who had a late trick up their sleeve.
Son could have been given offside when he challenged for Kieran Trippier's first cross but when a second delivery came in, he made it count, flicking the ball brilliantly through the legs of Heurelho Gomes to give the visitors a last-gasp victory.
TWEET OF THE MATCH
Son of a gun! Spurs may have pinched it! - @GaryLineker revels in Tottenham's late goal.
Heurelho Gomes - 5 (out of 10)
Miguel Britos - 5
Jose Manuel Jurado - 5
Troy Deeney - 6
Craig Cathcart - 5
Nathan Ake - 4
Ikechi Anya - 6
Almen Abdi - 5
Ben Watson - 5
Odion Ighalo - 7
Etienne Capoue - 6
Allan Nyom - 6
Sebastien Prodl - 5
Valon Behrami - 5
Hugo Lloris - 6
Danny Rose - 6
Toby Alderweireld - 6
Jan Vertonghen - 6
Harry Kane - 6
Erik Lamela - 7
Eric Dier - 6
Kieran Trippier - 6
Mousa Dembele - 5
Dele Alli - 5
Tom Carroll - 5
Son Heung-min - 6
Nacer Chadli - 6
Christian Erikson - 6
Erik Lamela: Had an impressive game for the away side and could have scored on a number of occasions aside from his opener. Watford's defence found Lamela a handful all afternoon, with Nathan Ake eventually seeing red for his high tackle on the Spurs midfielder.
MOMENT OF THE MATCH
Watford were forced down to 10 men when 20-year-old defender Ake, who is on loan from Chelsea, went in with a studs-up challenge on Lamela. Replays showed referee Anthony Taylor had no choice but to send him off; After an even game the Hornets struggled for the last half an hour to keep hold of the ball.
VIEW FROM THE BENCH
Mousa Dembele's first-half injury caused Mauricio Pochettino some issues but he chucked on Cristian Eriksen who impressed, but it was Son - another Pochettino sub - who won the day.
MOAN OF THE MATCH
Watford fans spent most of the afternoon booing referee Anthony Taylor but the man in charge managed to keep a feisty game under control for most of the match. Despite the protests the red card decision was spot on, with Lamela lucky not to be injured by Ake's challenge.
WHO'S UP NEXT?
Everton v Tottenham (Barclays Premier League. Sunday January 3)
Watford v Manchester City (Barclays Premier League, Saturday January 2)