Alejandro Garnacho and Casemiro struck twice in six first-half minutes to put United in control of the tie. Garnacho powered home from Diogo Dalot’s flat cross before Mason Mount provided a pinpoint corner for Casemiro to head home.
Erik ten Hag had made seven changes to the side that won 1-0 at Burnley with the likes of Bruno Fernandes, Marcus Rashford and Rasmus Hojlund moving to the bench with one eye on Saturday’s Premier League game with the same opposition.
Mount was subbed at half time for Victor Lindelöf with Ten Hag keen to manage the player’s minutes after his return from injury.
Anthony Martial sealed the win for United 10 minutes into the second half as he finished brilliantly at the back post from Casemiro’s cross. The fourth round draw will take place tomorrow night after Manchester City’s clash at Newcastle United.