Chances were few and far between in the first half, as the two sides failed to assert their supremacy on the game.
Darren Pratley tried to make the breakthrough for Bolton in the fifth minute when he took a shot from just outside the Watford box, but saw his effort go over the Bolton crossbar.
Cristian Battocchio went close for Watford just before the half-hour mark, but failed to hit the target with a shot taken from just outside the area.
However, Watford were soon 1-0 down thanks to a penalty from Marvin Sordell in the 32th minute.
Abdi himself scored the winning goal for Watford 20 minutes from time, firing home from close range after being set up by Vydra.