Odejayi managed to miss a chance against Cardiff in Sunday’s FA Cup semi-final defeat at Wembley after having a whole half to run into and, despite missing another howler, did manage to steer the Tykes deservedly ahead before the break.
Jonathan Macken drove a ball across Richard Lee to Odejayi, who tapped in from two yards out (36).
Captain Stephen Foster then headed in a second two minutes after the break before Odejayi produced an accomplished finish on 54 minutes to triple his league tally for the campaign and dent the Hornets’ chances of automatic promotion.
The win moves Barnsley out of the drop-zone and up four places in the table, relegating Colchester in the process. Watford remain fifth.