Adrian Mariappa's late own goal gave Cardiff City a point as former Watford boss Malky Mackay returned to his former club.
Cardiff dominated the first half but fell behind when Prince Buaben arrowed the ball home from just inside the box after Marvin Sordell's pass.
However, after a long throw that Scott Loach failed to clear, Mariappa turned the ball into his net.
Watford's Michael Kightly went close late on with a glancing header.
But Watford would have been satisfied with the result after the visitors dominated for long spells. The home team's unbeaten run has now stretched to seven matches, the longest current sequence in the Championship.
Early on, Filip Kiss delivered for Don Cowie but his guided header was brilliantly tipped wide by Loach. But Cardiff took control with Mark Hudson heading over from Peter Whittingham's corner.
Andrew Taylor then crossed for Whittingham, whose first-time shot crashed off the inside of the post and bounced into the arms of Loach.
There were further warning signs for the hosts after the break as Whittingham advanced unopposed before rifling in a dangerous shot that was deflected wide.
Watford took the lead against the run of play as Sordell set up Buaben, who opened his account for the club after 62 minutes.
With a renewed confidence Watford pressed again and, when Sordell was fouled on the edge of the box, the home crowd were baying for a red. Taylor escaped with a yellow.
Just as City were appearing to fade, they were handed a way back into the match when Loach raced out to deal with a long throw and the ball clipped off Mariappa and into the net.
Watford manager Sean Dyche: "I think, pretty much, we've done a good job today. But a lack of communication on a single moment is sometimes how a game can change.
"Cardiff started very brightly for the first 15 or 20 minutes and really loaded it on top of us with corners and long throws, as they did for the first five minutes of the second half.
"Other than that I thought we did very well in the game. The manner the lads are playing at the moment is terrific."
Cardiff manager Malky Mackay: "I thought we started very well and had five or six great chances at their goal in the first half, which I thought led a charmed life.
"On another day we would have gone in a couple up at half-time but we weren't clinical with them.
"What I was delighted about was the calmness of the boys to keep playing, keep believing and knowing we would get chances. It came, we scored from it."