Rene Gilmartin's error from Ashley Barnes' first-half strike was enough to hand npower League One leaders Brighton a surprise 1-0 victory at Championship outfit Watford in their FA Cup fourth-round clash.
In a game of few clear cut chances, Gilmartin should have easily saved Barnes' 20-yard effort, which came straight at him, but the Hornets goalkeeper spilled the ball into the net.
An uncharacteristically subdued Watford side nearly fell further behind but Gilmartin managed to make a fine save from Chris Wood's strike.
The striker then headed against the crossbar after the interval before the hosts finally asserted themselves.
The closest they came to an equaliser was substitute Will Buckley's strike from 12 yards, which was parried by Peter Brezovan.
Danny Graham missed the target with a couple of opportunities as Watford pushed forward for an equaliser but Brighton valiantly held on to claim a place in the last 16.