Liverpool's frustration was summed up on the half-hour, when Trent Alexander-Arnold sent an aimless first-time cross straight out of play.
Skipper Jordan Henderson threw down both his arms at another opportunity squandered by the visitors, in what amounted to an uncharacteristically-sloppy performance from Jurgen Klopp's side. While United, full of endeavour and enterprise, were unrecognisable from the lamentable displays against Brighton and Brentford, Klopp's men continued their curiously-sluggish start to the season.
James Milner ceded possession on numerous occasions in the first half, with Liverpool's midfield three of him, Henderson and Harvey Elliott lacking fluency and understanding.
Alexander-Arnold epitomised Liverpool's wretched display. Lucky not to be booked for a cynical early trip on Marcus Rashford, he was eventually cautioned for hauling down Anthony Elanga.
He was culpable early on when Elanga got in behind him, only to thud the ball at a post, and was caught flat-footed when the United winger exchanged passes with Christian Eriksen then crossed for Jadon Sancho to open the scoring.
For all his assists and occasional goal threat, Alexander-Arnold remains a liability defensively, and it was clear from the start United had targeted him as Liverpool's weak link down their right.
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Elanga, brought into the starting line-up in place of the benched Cristiano Ronaldo, tormented Alexander-Arnold early on with his pace and direct running, turning the England man inside out.
Quite why Klopp chose to start without Fabinho, arguably his most accomplished defensive midfielder, only he knows, but Liverpool suffered without his authority and composure in the middle. The Brazilian was eventually introduced just before the hour mark.
There was mitigation, of course, with Klopp missing Thiago, Diogo Jota, Joel Matip, Ibrahima Konate, Curtis Jones and the suspended Darwin Nunez, but Liverpool have suffered their worst start to a season for a decade and are already playing catch-up in terms of challenging for the title.
