Ole Gunnar Solskjaer’s permanent appointment ended with them taking the three points but they were a long way from their best.
United made a slow start but managed to score when it mattered with Rashford scoring in the first half and Martial doubling his side’s lead in the second.
Watford scored what proved to be a consolation goal through Abdoulaye Doucoure.
Just as in the first half, there was a timely goal to release the pressure as Anthony Martial scooped home at the second attempt after Jesse Lingard had squared a low pass to him from the right. It is not an afternoon that will live long in the memory for anything other than the reception for Solskjaer before kick-off, but the Frenchman at least ensured that United would get the result they needed.
MATCH FACTS AND STATS
MANCHESTER UNITED (4-3-3): De Gea; Young, Smalling, Jones, Shaw; Herrera (Pereira 63), Matic, Pogba; Mata (Lingard 63), Rashford, Martial (Rojo 77)
Subs not used: Romero, Lukaku, Fred, Dalot
Goals: Rashford 28, Martial 72
WATFORD (4-4-2): Foster; Janmaat (Femenia 55), Kabasele, Britos, Masina; Doucoure, Capoue, Hughes (Success 81), Pereyra; Deulofeu (Gray 73), Deeney
Subs not used: Gomes, Cathcart, Quina, Holebas
Goal: Doucoure 90
Booked: Hughes, Masina
Referee: Stuart Attwell (Warwickshire)