Spurs - who play a level below in the FA Women's Premier League - flew out of the traps and were 2-0 up inside six minutes at Cheshunt, Katie O'Leary adding the second.
Watford responded through Otesha Charles, Katie O'Leary made it 3-1 but Guyana international Charles had the final word by completing her hat-trick for 3-3.
Spurs remain unbeaten in pre-season after friendlies against Enfield, Middlesbrough, Arsenal's development side and Watford.
Having beaten Arsenal on Wednesday, this week has ticked all the pre-season boxes for manager Karen Hills.
"This performance is certainly another step forward for us," said Karen.
"It was a first 90-minute run for a few of the players and you have to remember we're still in pre-season whereas Watford are halfway through their WSL programme and right up to speed in terms of fitness.
"It was an ideal pre-season match for us, a physical test against a WSL team and we were disappointed not to win. It's all positive."
Below: Nikita Whinnett
SPURS 3-3 WATFORD
Report from Khalid Karimullah at Cheshunt FC
Following last week's friendly win against Arsenal Ladies’ development side, Spurs welcomed WSL2 outfit Watford Ladies to Theobalds Lane looking to build more pre-season momentum.
It took Spurs just 15 seconds to open the scoring. Bianca Baptiste broke away down the right flank and played in a low cross for Nikita Whinnett to open her account in our colours.
Six minutes later it was 2-0. Sophie McLean found Whinnett and her cross found Katie O’Leary who skilfully backflicked the ball over Lucy Gillett.
O'Leary, Lucia Leon and Baptiste all went close but just before the break, Otesha Charles kept possession with neat footwork inside the six-yard box before slotting home.
Spurs were quickly on the front foot in the second half. Gillett kept Baptiste at bay, Megen Lynch denied Charles at the other end and it was soon 3-1 as Whinnett played in Kelley Blanchflower, who took the ball past Gillett before rolling home just after the hour.
However, Watford turned the game around in a five-minute spell. Charlotte Kerr released Charles for 3-2 from close range before Charles completed her hat-trick on 72 minutes.
Watford’s quickfire double didn’t take the fizz out of Spurs, who almost restored their lead as Whinnett’s cross found O’Leary, but she couldn’t get a full connection on her half-volley.
Spurs Ladies: Toni-Anne Wayne, Lucia Leon, Alex Keown, Jenna Schillaci, Sophie McLean, Maya Vio, Riana Soobadoo, Josie Green, Katie O’Leary, Nikita Whinnett, Bianca Baptiste, Megen Lynch, Renee Hector, Kelley Blanchflower.