WATCH: Salah nets hat-trick as Liverpool humiliates 10-man United

United's poor start to the season hit a potential nadir on Monday (AEDT) as Liverpool ran riot at Old Trafford.

Mohamed Salah became the first Premier League player to score an away hat-trick against United, with Naby Keita and Diogo Jota having put Jurgen Klopp's team in control inside the opening 15 minutes.

Paul Pogba came on from the bench for a calamitous 15-minute cameo in which he conceded possession for Salah's hat-trick goal before seeing red for a lunge on Keita, though United at least managed to keep the Reds out while down to 10.

Having seen their team go into half-time 4-0 down for the first time in a Premier League game, United's fans let their feelings known as the players and Solskjaer walked off, and the atmosphere hardly improved after the final whistle.

Solskjaer appears to be under mounting pressure, with United relying on last-minute winners to see off Villarreal and Atalanta in the Champions League in recent weeks, while they have lost three of their last four top-flight matches, conceding 11 times and scoring just three in return.

"It is not easy to say something apart from it is the darkest day I have had leading these players," a dejected Solskjaer told Sky Sports.

"We were not good enough individually and as a team, can't give a team like Liverpool those chances but unfortunately we did.

"The whole performance was not good enough. We created openings, they had chances and they have been clinical. The third goal decided the game."

Asked who had to take responsibility, Solskjaer said: "It is mine, that is it. The coaching staff are very, very good, brilliant.

"I choose the way we approach the game, we were not clinical enough and gave too much space and when you give good players space they score."

United decided to try and press Liverpool from the off, a tactic that swiftly proved naive, though Solskjaer did not regret his approach. 

"We are at home, playing against Liverpool, we have gone here over the last two and half years and had a similar approach to high press but today they scored on their chances I think as United we should always try to stamp our authority on the game," he said.

"That fourth goal is when you go into half time with having to score one every 15 minutes. I know these boys are capable of it. The fourth, that was probably game over.

"You can look at last season we lose to Spurs 6-1 this is worse, miles worse. This is miles worse for me as a Manchester lad. I've just got to say we have to get over this as quickly as we can."

Solskjaer knows questions over his future will only increase, but he insisted he is in no mood to give in.

He said: "I have come too far, we have come too far as a group. We are too close to give up now.

"It is going to be a difficult one. The players will be low but there's loads of characters there. We know we are rock bottom, we can't feel any worse than this. Let's see where we take it."