Malky Mackay was denied a winning start as Watford boss after Doncaster striker James Hayter cancelled out Danny Graham's early strike.
Debutant Graham put the hosts ahead just before the half-hour mark when he nudged home Tommy Smith's wayward shot.
The visitors levelled before the break when Hayter met Brian Stock's cross and looped his header over Scott Loach.
Ross Jenkins, Scott Severin and Smith had chances to win the game for Watford but all failed to find the net.
Both sides struggled to create clear-cut chances but Doncaster boss Sean O'Driscoll will have gone home the happier of the two managers.
O'Driscoll, who opted against starting any of his summer signings, will have been particularly pleased with veteran goalkeeper Neil Sullivan.
As Watford pressed for a winner in the later stages of the game Sullivan was tested on several occasions, saving a tame effort from Adrian Mariappa before pulling off an assured stop from Smith's drive.
Meanwhile Mackay, who handed debuts to midfielder Severin and striker Graham, will be left to rue the lack of cutting edge which left his side with only a point.
Watford manager Malky Mackay: "I was pleased with the effort in the second half. They went out and were really positive.
"What I asked them to do in the second half was really press them and go out them and push forward.
"I was delighted with the effort in the second half and the way that with five, 10 minutes to go we were still pressing and pushing on."
Doncaster manager Sean O'Driscoll on a shot by Dean Shiels: "We've got a tape of the game and it's clearly over the line.
"It's a difficult one to give. The linesman was 40 yards away and the referee's in line with it, but until you get cameras on the goalline it's one of those that you've got to take on the chin.
"I think we can both play a lot better than we showed. It was extremely hot, and the game was in fits and starts throughout the 90 minutes."
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