Much-changed United hit four again and eased past division-lower Burton Albion to set up a Carabao Cup fourth round tie at Swansea.
The rotated Reds made nine changes from the weekend's win over Everton but still featured eleven international and had too much for Nigel Clough's team - who themselves made wholesale alterations.
Marcus Rashford's superbly-taken brace put United in control inside 15 minutes, before Jesse Lingard's deflected effort was added to by Anthony Martial after the interval.
To their credit, the Brewers became the first side to breach United's defence at home this season, through Lloyd Dyer's consolation at the death.
The Reds started well and took the lead after only five minutes when Lingard's flick-on fell to Rashford, and he finished smartly beyond Burton keeper Connor Ripley.
Ben Turner - who played in the 2012 final of this competition for Cardiff - blocked well from Lingard as United threatened to run riot against the second-tier side.
However, the respite proved only temporary as United quickly moved 2-0 to all but end the tie as a contest on 17 minutes.
Daley Blind broke forward from left-back and picked out Rashford, who collected the pass, swivelled and fired in a brilliant 20-yarder via a post.
Juan Mata hit a post and Martial - a constant menace throughout - had an effort blocked, before Burton almost caught United napping in a rare foray forward.
Joe Mason, also in that 2012 Cardiff squad, collected Luke Varney's pass and sent his lob goalwards, but United's stand-in stopper Sergio Romero saved well.
Martial was involved again in United's third goal of the night nine minutes before the break.
After he turned Tom Naylor inside out, he found the lively Lingard in space and the winger's effort took a deflection off Jamie Allen, wrong-footed Ripley and rolled in.
Martial capped his man of the match performance with a deserved goal shortly before the hour mark, when he fired home a finish from close range, having been played in by Rashford.
The Frenchman flashed a shot wide and Lingard also went close, with United youngsters Scott McTominay and Joel Pereira handed valuable run outs in the second half.
The visitors did at least go back to Staffordshire with a memento, however, when Dyer - their best player on the night - thumped in an angled effort after a goalmouth scramble in the final minute.
The draw for the last 16 was made immediately after the full-time whistle and pitted United with Paul Clement's Swansea for a place in the quarter-finals.
Overall team performance: 8/10
United Faithful Man of the Match: Anthony Martial