Erik ten Hag's team seemed down and out at the start of the season after a 2-1 defeat against Brighton and the subsequent 4-0 humiliation at Brentford.
A massive protest by United fans against the club's owners the Glazer family before Monday's game at Old Trafford added to the sense of despondency.
Marcus Rashford, Jadon Sancho and Anthony Elanga formed an attacking triumvirate that gave United the pace and energy they has previously lacked.
Defender Raphael Varane made his first start this season alongside new recruit Lisandro Martinez with Ten Hag's decision to drop captain Harry Maguire paying off.
United looked a completely different side as they created numerous chances.
Martinez has faced criticism for his performances in the opening two games but right from the outset, the Argentine left his mark on Mohamed Salah.
Playing alongside Varane, Martinez contributed to a solid display that showed none of the hesitancy and uncertainty of so many United performances at the back in the past year.
Dutch left-back Tyrell Malacia, making his first start since joining from Feyenoord, got over his early nerves to quickly win the appreciation of the home crowd with his tenacious tackling and tireless running.
With new signing Casemiro available for selection for Saturday's trip too Southampton on Saturday, things are starting to look up for United.
"Football, it's about energy, it's about when you have to push, when you have to stay calm, when you have to attack. We showed a great control. It was a mature performance," Varane said after the match.
"I really enjoyed it on the pitch, the atmosphere, the spirit of the team. I came to England to feel these emotions after everything I left in Madrid."
The new-found positivity was evident during training at Carrington. Cristiano Ronaldo was energetic as usual, even though he does not seem central to the manager's plans.
Ronaldo was reduced to a substitute appearance in the closing minutes at Old Trafford, allowing United to successfully deploy their manager's aggressive game plan.
However, Ten Hag insisted Ronaldo still has a future at United.
"In his whole career he did it under several managers, in several styles and systems. He always performed so why can't he do this? His age is not an issue," Ten Hag said after the Liverpool game.
"We have a squad and we have a way of playing, a style and a game plan. You look at what is the best approach to the game. Today it was those players, Saturday it could be different."