HEROLD Goulon's red card cost Doncaster dearly as Rovers ended the year in disappointing fashion - and were left propping up the Championship table.
Dean Saunders refused to defend Goulon after the on-loan Blackburn midfielder was sent off in the second half for two bookable offences.
His dismissal came just moments after Billy Sharp had nodded Rovers level and the visitors had the bit between their teeth at Vicarage Road.
But with ten men Doncaster looked dishelved and disorganised as Watford went on to win comfortably with goals from Marvin Sordell, John Eustace and Michael Kightly.
Sordell had put the hosts ahead at the end of a forgettable first half when he was allowed space to drive a shot past Gary Woods from the edge of the area.
But Rovers came out after the break looking a different side and within two minutes El Hadji Diouf crossed for Sharp to head home from close range.
Goulon, however, then saw red and it did not take long for the Hornets to reclaim their lead as Sordell's glanced header fizzed past Woods.
Substitute Eustace then drilled home from 20-yards with his first touch to kill off any chance of a Rovers comeback.
And Michael Kightly rubbed salt in the wounds when he was given the freedom of Vicarage Road to advance to the penalty area before stroking home a fourth.
The defeat left Rovers - who won just eight Championship games in 2011 - bottom of the table and five points adrift of safety.