On an evening where redemption was the special item on the menu, Marcus Rashford, Christian Eriksen and Alejandro Garnacho all scored braces, while Antony also netted a confidence-boosting penalty in an emphatic victory.
Red Devils fans have not become accustomed to seeing their side take control of proceedings and dominate for 90 minutes in recent times, and the calibre of opposition was certainly weaker, but Tuesday's result felt like another potential turning point after their impressive beating of Southampton at the weekend.
Rashford's fine finish, Antony's pinpoint penalty and Garnacho's slick toe-poke put the hosts in firm control before the half-time whistle blew, as their third-tier counterparts were left to lament some particularly atrocious defending.
Garnacho continued to steal the spotlight in the second half, bagging a double for himself before also setting up Rashford's second effort of the evening, with Barnsley still not learning their lesson defensively.
After Antony and Rashford's redemption goals, Eriksen notched two of his own in the space of a few minutes to rub salt into the wounds for Barnsley, who simply folded at the Theatre of Dreams as their hosts mercilessly ran riot.
MAN UNITED VS. BARNSLEY HIGHLIGHTS
Marcus Rashford goal vs. Barnsley (16th min, Man United 1-0 Barnsley)
The Rashford renaissance continues! Two goals in two games for the Englishman, who breaks the deadlock in clinical style.
The Red Devils work the ball to Rashford with just two cross-field passes, the latter of which sees Alejandro Garnacho pick out his senior colleague, who skips past a white shirt and thumps the ball into the roof of the net.
Antony goal vs. Barnsley (35th min, Man United 2-0 Barnsley)
Two redemption arcs being written this evening? The hosts win a penalty as Antony is brought down by Barnsley's on-loan Chelsea goalkeeper Gabriel Slonina.
The Brazilian steps up to the 12-yard mark and smashes his spot kick into the bottom corner after a stuttered run-up; Slonina dives the right way, but it is no use.
Alejandro Garnacho goal vs. Barnsley (45 +2 min, Man United 3-0 Barnsley)
Game, set, Garnacho. Rashford is involved heavily again, weaving his way through the Barnsley defence before being tackled, but the ball falls kindly into the path of his Argentinian colleague.
From a few yards out, Garnacho coolly taps the ball into the far corner of the net to surely seal the Red Devils' spot in round four.
Alejandro Garnacho goal vs. Barnsley (50th min, Man United 4-0 Barnsley)
A double for Alejandro, and Barnsley's evening has just become that little bit more chastening, but once again, the Tykes have done themselves absolutely no favours defensively.
Take nothing away from the lovely passing move, though, as Christian Eriksen picks out the run of Garnacho, who has nothing but turf ahead of him and bursts through on goal, before opening up his body and curling home past a stranded Slonina.
Marcus Rashford goal vs. Barnsley (58th min, Man United 5-0 Barnsley)
It just gets better and better for the rejuvenated Rashford. Garnacho plays provider this time, slipping in the Englishman down the perennially exposed left-hand side, and Rashford comfortably slots the ball into the bottom corner at Slonina's near post.
Christian Eriksen goal vs. Barnsley (81st min, Man United 6-0 Barnsley)
Six of the best for Man United, and it is just far too easy down the left-hand side again. Garnacho is involved - of course he is involved - as he slips in Bruno Fernandes on the left-hand side of the box.
The Portuguese cuts back for fellow midfielder Eriksen, who comfortably dispatches into the roof of the net at Slonina's near post.
Christian Eriksen goal vs. Barnsley (85th min, Man United 7-0 Barnsley)
Fernandes to Eriksen again. Man United score again. Barnsley are heading home as battered and bruised as they could possibly be.
The Red Devils' skipper lays off his Danish foe with a light touch on the edge of the area, and Eriksen wastes no time in firing the ball into the far corner to put the hosts in seventh heaven.
MAN OF THE MATCH - ALEJANDRO GARNACHO
Even though Rashford, Antony and Eriksen all deserve their rightful plaudits, Garnacho once again proved why there is all the hype around him with a masterful display against an admittedly horrendous defence.
The South American took his finishes well and was as much of a prolific playmaker as he was a goal-getter on the night, laying on two assists to complete a near-perfect performance.
MAN UNITED VS. BARNSLEY MATCH STATS
Possession: Man United 65%-35% Barnsley
Shots: Man United 26-3 Barnsley
Shots on target: Man United 13-0 Barnsley
Corners: Man United 3-1 Barnsley
Fouls: Man United 16-11 Barnsley
WHAT NEXT?
Man United must wait a week to learn their fourth-round opponents, as the draw will not be made until the third-round ties have finished on September 25, but Ten Hag's immediate focus is on this Saturday's Premier League trip to Crystal Palace.
Meanwhile, Barnsley have three full days to dissect Tuesday's crushing loss before travelling to Burton Albion in their next League One battle.