Ten Hag picked a vastly more experienced team than Jurgen Klopp and it paid off with United racing into a 3-0 lead after barely half an hour thanks to goals from Jadon Sancho, Fred and Anthony Martial.
Klopp made a raft of substitutions on 30 and 60 minutes while Ten Hag made 10 changes at half-time and the Dutchman's second string increased United's lead late on through Facundo Pellistri.
Liverpool, who started with a mixture of first-teamers and youngsters, started brightly in front of 50,248 fans at the Rajamangla National Stadium and David De Gea was twice called into early action, first to block Isaac Mabaya's cross and then to save at full stretch from Luis Diaz.
But after 12 minutes United were ahead when Mabaya failed to clear Bruno Fernandes' cross and Sancho whipped in a first-time finish with his right foot.
Liverpool hit the post twice in quick succession through Fabio Carvalho -- making his debut following his move from Fulham -- and Diaz soon afterwards but the end of the first half was dominated by United.
Fred made it 2-0 on 30 minutes with a wonderful clipped finish which sailed over Alisson before Martial -- back at the club after a loan spell at Sevilla -- robbed Rhys Williams on the sideline to race towards Alisson and score for United for the first time since October.
Diogo Dalot almost made it 4-0 before half-time but struck the underside of the bar.
Klopp waited until the final 30 minutes to throw on his big hitters including Virgil van Dijk, Thiago, Mohamed Salah and new £85 million striker Darwin Nunez and although Nunez forced De Gea's replacement, Tom Heaton, into a good save it was United who scored again on 77 minutes when Pellistri finished off a slick counter-attack started off by a surging run from Eric Bailly.
Salah almost pulled one back but saw a curling effort with his left foot come back off the post before Nunez blasted the rebound over the top.