The hosts led 3-0 by the break after goals from Lucia Garcia, Alessia Russo and Hayley Ladd.
United cruised to victory as Martha Thomas, Rachel Williams and an Emma Koivisto own goal increased their tally to six.
Marc Skinner’s side are now second, three points behind leaders Chelsea with a game in hand.
Go straight to our Women’s Football page
Reaction to Man Utd’s victory over Liverpool
United started their first game of 2023 in fine fashion as Garcia coupled with fellow Spain international Ona Batlle to put her side in front in the sixth minute – Garcia’s goal-bound effort taking a wicked deflection off Gemma Bonner as it got the better of Liverpool goalkeeper Rachael Laws.
Marc Skinner’s side started well and placed the visitors under continual pressure with Hannah Blundell narrowly missing out on doubling United’s advantage minutes later as she shot wide when left free inside the box.
They got their second of the afternoon after a Liverpool error; Ella Toone taking advantage as Ladd dispossessed a visitors player to thread through to Russo, who tucked her excellent first-time finish into the bottom corner.
Ladd then made it three as she redirected a pinpoint lofted Batlle ball past Laws.
Liverpool were much-improved in the second half and won a number of set pieces in dangerous positions.
But their improvements did not dent United’s swagger and they made it four after Emma Koivisto turned a Millie Turner effort into her own net before substitute Martha Thomas added a fifth from close range.
Rachel Williams added another nail in the coffin for Liverpool in the 84th minute, nodding home Ladd’s cross.