The 1-1 stalemate was a fair result, but Sean O'Driscoll's visitors will be more content with the outcome.
After Rovers had made the brighter and more composed start, it was Watford who scored their first goal of the season in the 27th minute.
The Doncaster defence failed to clear a Don Cowie free-kick from just outside the left of the penalty area, the ball ran through to last season's top scorer Tommy Smith.
His scuffed cross-shot fell perfectly for new boy Danny Graham to tap home from barely two yards out and start repaying the £200,000 initial payment a Football League tribunal ruled the Hornets need to give Carlisle United earlier in the week.
But the visitors were back on terms 11 minutes later thanks to a goal that was superbly executed, if a little fortuitous.
There appeared to be no danger when Brian Stock clipped a ball towards the edge of the area from the left, but James Hayter got in front of Lloyd Doyley to send a looping header over England Under-21 keeper Scott Loach from all of 16 yards.
Doncaster were unfortunate not to take the lead 12 minutes after the restart when a Stock corner from the right was flicked on and Dean Shiels thought he'd squeezed the ball over the line at the far post, but Loach got his arm down just in time to keep the opportunity out..
But the Hornets were not far away with 20 minutes remaining when Smith pulled off his man on the edge of the six-yard box to head an Adrian Mariappa long throw narrowly wide of the far post, with keeper Neil Sullivan beaten.
The Doncaster keeper's goal came under the greater pressure in the closing stages, but Watford were unable to muster a clear-cut opportunity.