After a desperately poor first half, the game sparked into life in the 53rd minute as Abdoulaye Doucoure scored a comical own goal to hand the visitors the lead.
That setback only served to motivate Javi Gracia's side, who stormed back with two headed goals from Troy Deeney and Craig Cathcart in the space of seven minutes to join Liverpool and Chelsea on maximum points from the opening four games.
It was a result that brings Spurs, who had won their opening three matches, crashing back down to earth following Monday's 3-0 win over Manchester United.
During a tepid opening both sides exchanged headed chances, Dele Alli guiding his wide of Ben Foster's post and Deeney powering one over the crossbar from just six yards out.
Tottenham looked the most threatening for the remainder of the half, but their only real chance came a minute before the interval when Davinson Sanchez headed over Jan Vertonghen's teasing cross from the left.
Christian Eriksen signalled Tottenham's intent at the start of the second period, firing in long-range drives that were held by Foster, before Doucoure's slapstick intervention handed Spurs the lead.
Foster looked primed to collect a looping ball before Christian Kabasele headed it almost out of his hands and into the path of Lucas Moura, whose delivery back across goal was chested into his own net by the hapless Doucoure.
This woke Watford from their slumber and they almost levelled after 67 minutes when Toby Alderweireld headed against his own crossbar before Deeney nodded in from Jose Holebas' fine free-kick shortly after to level things.
Holebas turned provider again for the winner in the 76th minute, his outswinging corner wonderfully headed into the top corner by Cathcart to continue his side's remarkable start to the season.
FT | #watfordfc 2-1 @SpursOfficial
WHAT A WIN!!!!! COME ON!!!!#WATTOT
Listen live :arrow_heading_down:https://t.co/GtJifEzTES pic.twitter.com/F9DcdpGVXU — Watford Football Club (@WatfordFC) September 2, 2018
What it means: Watford in dreamland
Cathcart's header means that Watford have won their opening four games in a league season for the first time since the 1988-89 campaign. Tottenham's start has still been a strong one with nine points out of 12, but they will go into the international break furious that they threw this one away.
Pat on the back: Deeney the destroyer
Deeney's weight loss has been well publicised recently and it is clearly paying off for the forward. He was unstoppable in the second half and scored the crucial leveller that paved the way for a wonderful win.
Boot up the backside: Kane not so able
He is up and running in terms of goals this season, but questions have been raised about Harry Kane's general fitness. He once again looked off the pace and never looked like threatening the Hornets' backline.
Key Opta stats:
- Troy Deeney became the fourth player to score in 100 matches for Watford in all competitions, after Tommy Barnett, Ross Jenkins and Luther Blissett.
- This was the first time that Tottenham lost a game in which they had been leading in the Premier League since November 2016 against eventual champions Chelsea, ending a run of 48 league matches without defeat when taking the lead at any stage.
- This was Watford's first league win over Tottenham since May 1987, ending a run of 12 league games without a victory over the Lilywhites (D4 L8).
- Since Javier Gracia took over as Watford manager in January, no side has won more home Premier League games than the Hornets (seven, level with Arsenal, Liverpool, Manchester City, Manchester United and Spurs).
100 - Troy Deeney has become the fourth player to score in 100 matches for Watford in all competitions, after Tommy Barnett, Ross Jenkins and Luther Blissett. Legend. pic.twitter.com/vSDWuSA1zr — OptaJoe (@OptaJoe) September 2, 2018
Watford host Manchester United at Vicarage Road after the international break, while Tottenham have a mouth-watering contest to look forward to as Liverpool pitch up to Wembley.