Red Devils fans slammed the big Belgian midfielder.
Daniel Sturridge fired the Reds ahead from the penalty spot on 20 minutes, before Roberto Firmino added a second in the final quarter as Jurgen Klopp's side placed one foot in the next round.
It was a disappointing night all round for the visitors, who did have a hero in the form of David de Gea, the Spaniard being his usual brilliant self for the full 90 minutes.
There was, however, also a villain of the piece for United fans, who slammed Marouane Fellaini for his overall display on Twitter afterwards.
The big Belgian was also perhaps fortunate to stay on the field after aiming an elbow at Emre Can in the dying minutes in an incident which might see him slapped with a retrospective ban.
Louis van gaal deserves a horrible death for playing Fellaini full time— Demmie (@d1_homid) March 10, 2016
Hate Fellaini— James (@JamesHussyy) March 10, 2016
I hope Fellaini gets a ban for that elbow.— Aditya Sanchez (@AdityaBaller) March 10, 2016
How do you give Fellaini 90 mins— Sir Masco™ (@Sir_masco) March 10, 2016
Fellaini role tonite? All balls to him. He can't hold d ball, can't tackle, can't control d ball & he's on 4 90mins https://t.co/JKuuBAYR85— Moses Nosa Omede (@NosaOmede) March 10, 2016
What at all did Fellaini do in the match? Someone tell me. Maybe I wasn't watching the game well— Fibonacci (@luwi_i_am) March 10, 2016
How is fellaini a united player? Not even a united material #LVGOut— Barkawi ™ (@ItsBumaye_) March 10, 2016
@Fellaini please leave Utd, that performance tonight was an embarrassment to the Utd shirt— Justin Long (@jut74) March 10, 2016
@8ooth that's true, if fellaini plays next week I'll be amazed, he was awful tonight, he always is awful— Jack (@_JMConnor) March 10, 2016
In Fellaini's defence, it was the midfielder's first game back following a month-long absence through injury, though it is ever so hard to defend the incident with Can toward the end.