Doncaster only had themselves to blame after getting their tactics wrong at the start.
Manager Sean O'Driscoll switched to a system with three centre-backs and played with only one man up front.
But the safety-first strategy came unstuck when Watford scored twice in the first 18 minutes forcing the home boss to switch to Plan B.
Rovers sent on striker Dean Shiels for centre-back Sam Hird and immediately looked more threatening with the Northern Ireland international causing plenty of problems for the Watford defence.
But by then the damage had been done and it was Hird who had the misfortune to put Watford on the path to victory with an own goal in the 13th minute.
Tamas Priskin latched on to a long ball down the right and when his penetrating cross came over, Hird knocked it into his own net in his desperation to clear.
Rovers had produced the first threat earlier in the game when Martin Woods had a left-foot volley parried by keeper Scott Loach in the third minute.
But once they had taken the lead there was no stopping Watford and Priskin forced a fine save from Neil Sullivan moments after they had scored.
It was 2-0 in the 18th minute when Don Cowie was left unmarked to send a glancing header into the top corner after latching on to a splendid cross from Adrian Mariappa.
Rovers battled back strongly with Shiels going close three times before Will Hoskins missed a great chance to add a third for Watford in the 55th minute.
James Hayter scored a superb consolation goal for the home side with a magnificent angled shot from the edge of the box after dribbling through five minutes from time but it was too little, too late.