The Hornets made the short trip to west London knowing a win over a team already safe from the drop would ensure they too stayed up.
With his side no longer in danger, Rangers boss Neil Warnock was even considering blooding the club's youngsters over their remaining games.
But out of respect to the relegation scrap below - not least the struggles of his old club Crystal Palace - he made only two changes, bringing in teenager Antonio German and fellow striker Rowan Vine.
And their victory, courtesy of Buzsaky's first-half penalty, means the agony goes on for the Hornets who are still two points above the drop zone with two games to play.
The Hornets knew it was not going to be their night when another Sordell cross was prodded goalwards by Jon Harley five yards out, only for Cerny to somehow get in the way.
In the evening's other game, Scunthorpe produced a dramatic comeback inside the final 10 minutes to earn a vital point in a 2-2 draw with Reading that sees them nail down their Coca-Cola Championship safety.
Going into the game knowing a draw would suffice in their battle to avoid the drop, it looked as though they had spurned their opportunity when the Royals surged into a two-goal lead thanks to Alex Pearce's volley and a Gylfi Sigurdsson penalty.
But Scunthorpe produced a late rally that typified their endeavour, to sensationally draw level as Gary Hooper's close-range finish and a deflected Matt Sparrow effort sent Glanford Park into raptures and kept the Iron in the Championship.
The draw means that Scunthorpe go into the final two games of the campaign, contemplating back-to-back seasons in the second tier for the first time in 46 years.