Such is the volatile nature of the Championship 11th-placed Watford would overtake Preston, who are fifth, with a win on Tuesday night.
That may have seemed an unlikely scenario when Watford were 2-0 down at Derby on Saturday before scoring twice in the final five minutes to complete a 3-2 comeback win.
Preston are looking to avoid going three league games without a win for the first time this season.
Watford lost this exact fixture 2-1 last season, last losing consecutive home league games against Preston in August 2005.