Paul Dickov tonight kept faith with his Doncaster Rovers side, sticking with the same starting XI that impressed in the goalless draw at Huddersfield last weekend.
But a penalty with minutes left, robbed Rovers of a Championship point.
The only change to the Rovers squad saw loan signing Federico Macheda named on the bench in place of fellow striker Billy Paynter.
The Manchester United man came on in the second half for an out of sorts David Cotterill.
Watford boss Gianfranco Zola had rung in the changes with six players dropping out of the side that drew 1-1 with Charlton on Saturday. In came Joel Ekstrand, Cristian Battocchio, Lloyd Doyley, Javier Acuna, Ikechi Anya and Connor Smith.
Theo Robinson almost got Rovers off to a flying start, but his header went wide on three minutes.
And Rovers seemed full of purpose, until they went behind on 13 minutes, when Lewis McGugan chipped the ball over Ross Turnbull.
But then they were level almost straight away with Chris Brown cashed in on a goalie fumble.
It was a fitting reward, considering the amount of possession Donny had enjoyed.
But it took a smart save from Turnbull to deny Cris Battocchio.
There were chances at either end too for James Husband and Javier Acuna.
After the interval, the Hornets started to exert some pressure and Rob Jones was a notable leader in the visitors’ rearguard.
James Coppinger almost put Rovers ahead but fired over.
And Watford sub Fernando Forestieri almost made a differnce when he came on but his effort was wide of target.
Then there were chances for Robinson and Coppinger - but neither hit the net.
The home side were awarded a penalty though, with four minutes to go, after James Husband fouled Sean Murray.
Turnbull went the right way but McGugan just managed to beat him.
Watford will have thought their second half period justified the winner.
Watford: Manuel Almunia, Lloyd Doyley, Gabriele Angella, Joel Elkstrand, Ikechi Anya, Cristian Battocchio, Connor Smith, Lewis McGugan, Daniel Pudil, Troy Deeney, Javier Acuna.
Subs: Jonathan Bond, Essaid Belkalem, Fernando Forestieri, Sean Murray, Davide Faraoni, Diego Fabbrini, Iriney.
Rovers: Ross Turnbull, Reece Wabara, Bongali Khumalo, Rob Jones, James Husband, David Cotterill, Paul Keegan, Richie Wellens, James Coppinger, Chris Brown, Theo Robinson.
Subs: Jon Maxted, Paul Quinn, Luke McCullough, Dean Furman, Mark Duffy, Kyle Bennett, Federico Macheda.
Read Liam Hoden’s analysis in The Star and the Doncaster Free Press.