Jesse Lingard ended a stirring second-half comeback from Watford as Manchester United escaped from Vicarage Road with a tense 4-2 victory.
England international Lingard scored a tremendous solo goal in the 86th minute to sting the Hornets, who set up a tense finale by rallying from three goals behind with just 13 minutes remaining.
Ashley Young returned to haunt his former club and ended a 560-day wait for a United goal with a first-half double, while Anthony Martial took advantage of a more central role afforded by Jose Mourinho's switch to a three-man defence with his eighth strike in all competitions this season - matching his tally from last term.
Romelu Lukaku wasted a glorious chance to mark his 200th Premier League appearance with a goal as his struggles in the box continued, but Watford captain Troy Deeney made no mistake from the spot on his return from a three-match ban for violent conduct.
Abdoulaye Doucoure boosted what had seemed an unlikely comeback when he struck six minutes from time, but Lingard capped an impressive display in the number 10 role with a stunning effort moments later.
That secured United's first win in four Premier League away games closed the gap to leaders Manchester City, who face Southampton on Wednesday, to five points.
Richarlison looked eager to continue his impressive form in the opening 10 minutes but it was a former Watford star that got the opening goal.
After some excellent hold-up play from Lingard, Young's first touch beat Kiko Femenia and his second was a rifled finish into the bottom-left corner.
Young doubled his tally in similarly sumptuous fashion just six minutes later by curling a magnificent free-kick beyond Heurelho Gomes after Doucoure's foul on Paul Pogba.
There was no let-up from United as Watford crumbled. Lukaku fed Christian Kabasele's poor attempt at a headed clearance straight to Martial, who made no mistake from the edge of the box to give the visitors a commanding lead just after the half-hour mark.
Gomes denied Lukaku and Lingard with a brilliant double-save before half-time, while Richarlison's header bounced behind off the crossbar in stoppage time.
Nemanja Matic appeared to be struggling with an injury as he made way for Ander Herrera in the 54th minute, while Will Hughes was replaced by Roberto Pereyra after appearing to sustain a hamstring issue. Marco Silva also sent Andre Carrillo on for Sebastian Prodl in an attacking switch, but there was no immediate galvanizing effect on Watford for the time being.
A loss of concentration saw substitute Marcus Rashford pick Adrian Mariappa's pocket and set up Lukaku for what looked like a simple finish, but the striker looked a man short of confidence as he hesitated before seeing his eventual shot blocked by Mariappa.
Watford reduced the arrears when Deeney, who replaced Andre Gray in the 72nd minute, slid a penalty into the bottom-left corner, and United were soon under greater pressure.
Doucoure stabbed home his fifth goal of the season with six minutes remaining after a touch from substitute Andre Carrillo, but there was to be no remarkable comeback.
Lingard picked up the ball inside his own half and dribbled into the Watford box before sliding a cool finish beyond Gomes in a breathless finish.