All the goals in this fixture at Vicarage Road this afternoon were scored during the opening 45 minutes.
Watford's Mark Yeates opened the scoring after five minutes, but that lead was cancelled out soon after by Lee Frecklington.
A brace from Marvin Sordell opened up a two-goal advantage for the hosting Hornets, only for Emile Sinclair to reduce the arrears six minutes before the break.
Darren Ferguson's Peterborough searched for an equaliser after the break, but their quest ultimately proved unsuccessful as they slipped to a defeat.