Scott McTominay's fourth-minute header was enough to give Manchester United an unconvincing victory in their FA Cup third-round tie against Watford on Saturday.
Wearing the captain's armband for the first time in a much-changed side from Wednesday's Carabao Cup semi-final defeat by Manchester City, McTominay found the net after rising to meet Alex Telles' corner.
The hosts did have chances to increase their lead, but Juan Mata failed to find a finish to an excellent three-man move just before half-time, then Daniel James and substitute Marcus Rashford had shots saved after the break.
But none of those opportunities were better than that for Hornets defender Adam Masina, who saw his effort blocked by United keeper Dean Henderson not long after McTominay had struck.