Watford's relegation worries deepened after Leeds defender Clarke Carlisle won the visitors all three points.
Leeds went in front with a lovely goal from Rob Hulse, the big striker heading Gary Kelly's cross past Richard Lee.
The Hornets levelled before the break when Heidar Helguson nodded in after Brynjar Gunnarsson's shot was saved.
The game turned when Jay DeMerit was dismissed for two late tackles and Leeds took advantage, Carlisle heading in Matthew Kilgallon's cross to win it.
Watford: Lee, Doyley, DeMerit, Cullip, Chambers, Eagles (Young 72), Mahon, Gunnarsson (Dyer 79), Blizzard, Bouazza (McNamee 75), Helguson. Subs Not Used: Chamberlain, Cox.
Sent Off: DeMerit (50).
Booked: DeMerit.
Goals: Helguson 41.
Leeds: Sullivan, Kelly, Carlisle, Kilgallon, Gray, Johnson, Gregan, Derry, Lennon (King 66), Healy (Moore 27), Hulse (Richardson 88). Subs Not Used: Einarsson, Spring.
Booked: Carlisle, Healy.
Goals: Hulse 28, Carlisle 67.
Att: 16,306
Ref: N Miller (Co Durham).