Draw specialists Preston had the better of the early play with Jamaican international Ricardo Fuller having a couple of chances early on in the game.
In the third minute Erik Skora crossed the ball to Cresswell who flicked the ball on to Fuller who hit a right-foot shot which went past the right-hand post.
In the 22nd minute Dickson Etuhu burst through the middle before hitting a right foot-shot over.
Watford's first chance fell to Jamie Hand who hit a 25-yard shot straight at the Preston keeper. In the 18th mintue Tommy Smith was put through and his shot was also saved by Tepi Moilanen.
Watford made it 1-0 in the 31st minute when Paul Robinson intercepted the ball on the left wing and hit a 35-yard left -foot shot which bobbled past the static defence and went low into the bottom corner of the net.
Cresswell had a good backward header which narrowly missed the target early in the second half and also had a shot which went inches wide in the 66th minute.
Lloyd Doyley had a great shot from the left and the Preston keeper Moilanen made a brilliant save diving to his left to tip the ball away for a corner after a mistake by Preston right-back Graham Alexander.
Preston made their first and only substitution in the 69th minute withdrawing Michael Keane for David Healy.
The equaliser came in the 73rd minute when a Marlon Broomes throw-in from the left bounced up to Cresswell, who from a central position five yards out, headed into the bottom corner of the net.
This was his third recent late equaliser with his other goal being an injury-time winner.