The visitors looked like they might be in for a hard afternoon when some abject defending allowed Danny Graham to find Tommy Smith in plenty of space in the area in the area in the 23rd minute and the Hornets' top-scorer from last season finished confidently to make it 1-0.
Watford had the better chances thereafter - including when Don Cowie hit the bar from 25 yards - but the visitors were back on terms after 56 minutes.
Keeper Scott Loach was unable to hold a header from Jay Emmanuel-Thomas, who was making his first professional start, and Alex John-Baptiste followed in to equalise from close range.
Within seven minutes though, Watford were back in front.
Smith was the creator this time with his run and cross from the left picking out Tom Cleverley, who scored his second in as many appearance since signing on loan from Manchester United.
But the visitors refused to lie down and they pulled level for a second time with 18 minutes remaining when the impressive Charlie Adam squeezed in a cross from the right side of the penalty area and Gary Taylor-Fletcher was in the right place to convert from close range.
Blackpool, if anything, looked the more likely to win it in the closing stages, but it was the home side who went the closest deep into injury time when keeper Paul Rachubka excelled to touch a curling shot from John Eustace onto a post.
Fellow substitute Henri Lansbury, who joined on loan from Arsenal on Friday, was then unable to convert the rebound.