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.
Brazilian Richarlison looped a header against the crossbar for Watford, but Troy Deeney scored a penalty and Abdoulaye Doucoure poked home from inside the area with six minutes to go for a tense finish.
The Special One could not believe his eyes his wing-back found his first Premier League goals since a defeat or Bournemouth back in May 2016.
Watford head coach Marco Silva also sent on midfielder Andre Carrillo, shifting to a back four, and his side began to look more unsafe, Richarlison heading wide from another Femenia cross.
United slowly grew into the game, although they struggled to link up with Romelu Lukaku.
Making his third straight start in the Premier League, Young provided the opener in the 19th minute after receiving Lingard's pass at the top of the box and popping the ball up in the air with his first touch before sending a laser inside the near post.
Doucoure was booked for fouling Paul Pogba and Young clinically dispatched a 25-yard free-kick with unerring accuracy.
Injuries bit for both teams in the second half, Matic hobbling off for United, to be replaced by Ander Herrera, and Watford's Will Hughes giving way for Roberto Pereyra after injuring his hamstring.
Lukaku wasted a fine opportunity to add a fourth with 15 minutes remaining as he dawdled when picked out free in front of goal and eventually saw a shot blocked from an acute angle.
Doucoure looked to have made it a nervy final six minutes for United as he steered Andre Carrillo's cross past De Gea, only for Lingard to score a brilliant solo effort moments later to finally secure the points.