United were 2-0 down inside 13 minutes and 4-0 down by half-time with Naby Keita and Diogo Jota scoring and then Mohamed Salah netting a brace before the break to take his scoring run to 10 successive games across all competitions.
Salah became the first away player since 2003 to score a hat-trick at United after notching his third goal just five minutes into the second half.
Ronaldo thought he’d scored a consolation for United but saw a goal chalked off for offside while half-time substitute Paul Pogba was shown a red card just 15 minutes after coming on following a VAR review over a reckless challenge on Naby Keita.
Defeat for United leaves them eight points off leaders Chelsea after just nine matches of the Premier League season, having lost three of their last four top-flight outings.
And Ronaldo, who rejoined United from Juventus in the summer, has spoken out to address the team’s struggles following their heavy defeat to Liverpool.
The Portuguese forward admits he and his team-mates must accept blame for United’s below-par form as manager Ole Gunnar Solskjaer comes under huge scrutiny.
Ronaldo wrote on Instagram: “Sometimes the result is not the one we fight for. Sometimes the score is not the one we want. And this is on us, only on us, because there’s no one else to blame.
“Our fans were, once again, amazing in their constant support. They deserve better than this, much better, and it’s up to us to deliver. The time is now!”
Watch: Ronaldo kicks Curtis Jones