Substitute Marouane Fellaini scored in second-half stoppage time as Manchester United beat Valencia 2-1 in manager Louis van Gaal's first home game in charge of the English Premier League club.
Wayne Rooney had a first-half penalty saved in the 32nd minute having earlier been felled by defender Antonio Barragan.
United broke the deadlock early in the second half when Darren Fletcher slotted home from the edge of the area after Ashley Young's 49th minute corner.
The visitors pressed for an equalizer and were rewarded in the 71st when Rodrigo blazed a first-time volley into the roof of the net following a free-kick.
Substitute Pablo Piatti poked a shot wide from close range moments later and the La Liga side were left to rue that miss when Fellaini struck late on.