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.
Buzsaky has painful memories of the reverse fixture back in December, when his dressing-room bust-up with Jim Magilton led to the then manager's sacking.
Some four Rangers bosses later the Hungarian is now trying to nail down a place in Warnock's team.
He made a lively start with a 20-yard shot which flew over the bar and a free-kick which had Hornets keeper Scott Loach scrambling to save.
So when Dusko Tosic's 37th-minute charge into the penalty area was clumsily halted by Hornets right-back Adrian Mariappa, it was no surprise to see Buzsaky step up and tuck his 12th goal of the season past Loach.
Watford were looking like potential play-off outsiders when the teams last met, but a meagre four wins since has seen them plummet down the table.
While Rangers were able relax, the Hornets were a bundle of nerves with Loach's wayward kicking a concern for boss Malky Mackay.
When the visitors did get a sight of goal in the first half, Radek Cerny easily saved Henri Lansbury's free-kick and also a weak half-volley from the same player.
They did have the ball in the net nine minutes after the break, Ross Jenkins playing in Danny Graham for a neat finish, but not for the first time the striker was flagged offside.
Graham has scored just three times since Watford's poor run began at the turn of the year and he fluffed his lines in front of goal in the 64th minute, diving to meet an inviting cross from substitute Marvin Sordell but glancing his header a long way wide.
And 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.