Paul Pogba shone and Robin van Persie scored on his Old Trafford return as United moved second in Group A with an impressive win.
Two penalties in three first half minutes- converted by Pogba and then Anthony Martial- put the Reds in control before Pogba made it 3-0 with a superb 20 yarder on the stroke of the break.
Jesse Lingard drilled in the fourth to rubber-stamp the result but RvP's late consolation goal was cheered almost as loudly as Old Trafford rose as one to applaud our former hero.
Such a convincing scoreline looked unlikely after a sluggish start in which United had plenty of the ball but little in the way of chances.
Pogba was blocked off by ex Liverpool man Martin Skrtel before Martial was inches away by turning home a delightful cross from the excellent Juan Mata.
United had soon seized control, however, with two quick fire spot-kicks just beyond the half hour mark.
Michael Carrick picked out Mata with a pinpoint pass, the Spaniard went down under a challenge from Simon Kjaer and Pogba sent Volkan Demirel the wrong way from 12 yards.
French referee Benoit Bastien pointed to the spot again in United's next foray forward when, this time, Martial was bundled over by Sener and did the rest for his second goal of the season.
David de Gea saved well from Josef Souza but the Reds were rampant and surged into a three goal lead to put the result beyond doubt by half-time.
The recalled Wayne Rooney found Lingard who cut the ball back for Pogba to guide a superb 20 yard effort into the top corner for his second of the game.
Former West Ham winger Emmanuel Emenike came on at the break for the visitors- as did Marcos Rojo for the Reds- but any lingering hopes of an unlikely Fener comeback were quickly extinguished on 48 minutes.
Rooney picked out Lingard to lash past a stranded Demirel from the edge of the area for his first goal in Europe for the club.
Fener mounted a late rally and van Persie received a standing ovation from everyone inside Old Trafford when he marked his return with a goal as he tapped in Emenike's cross from close range.
De Gea pushed away Souza's effort from distance while Demirel denied Mata and substitute Tim Fosu-Mensah on a satisfying night for Mourinho and the team ahead of Sunday's league trip to Chelsea.
Overall team performance: 8.5/10
United Faithful Man of the Match: Paul Pogba