Substitute Anthony Martial opened the scoring, following a quick counter-attack, before Fred doubled the advantage after a great piece of build-up play to book the Reds a spot at Wembley against Newcastle United on 26 February.
United looked in total control and have now won 12 games in a row at Old Trafford after completing the job. Jadon Sancho made his return to the United side, coming off the bench to replace Antony to a warm ovation from the United faithful.
FIRST HALF - DOMINANT YET QUIET
The Reds stepped out onto the Theatre of Dreams to a thunderous cup semi-final atmosphere and this motivated United to control the game early, looking comfortable in possession but we did not get a significant attack until 10 minutes into the half.