His double inside the first 25 minutes means Rashford scored more goals from one game than Alexis Sanchez has managed for United since signing the most lucrative contract in Premier League history in January.
The Chilean’s arrival has pushed Rashford down the pecking order despite Sanchez’s struggles to recreate the form that made him so in demand when he decided to run down his contract at Arsenal.
Sanchez has just one goal in nine games in a United shirt.
Indeed, had it not been for an impact injury suffered by Paul Pogba in what Mourinho described as “the final minute” of training on Friday, there is every chance Rashford would have been sidelined once more.
Instead, Sanchez moved inside to an advanced midfield role Pogba would likely have filled to create the space on the left for Rashford to win the game.
“He scored two goals in a big match against a top class opponent,” said Mourinho. “Of course he was fundamental.”
His first goal in particular didn’t resemble a player short on confidence and without a goal in the league since early December.
Rashford burst onto Romelu Lukaku’s flick-on and turned inside Trent Alexander-Arnold before blasting past Loris Karius into the far corner.
– ‘We trusted him’ –
Boosted by breaking his drought, Rashford then swept home a second 10 minutes later with the Liverpool defence again scrambling after Lukaku had outmuscled Dejan Lovren.
“The good thing was the first chance he had, he got it, he scored because I think in the last two months that was not happening with him,” added Mourinho.
“Today, a big game, probably he didn’t expect it, but we trusted him and thought the game adapted to his qualities.”
Rashford’s return to form couldn’t have come at a better time not just for United — who face another two crucial games this week when Sevilla and Brighton visit Old Trafford in the Champions League and FA Cup respectively — but also for England.
England manager Gareth Southgate was among an impressed crowd just five days ahead of naming his squad for friendlies later this month against the Netherlands and Italy.
Those games will be Southgate’s last chance to experiment before naming his 23-man squad for the World Cup in Russia.
“It was nice that he was here to watch but there are a lot of players in contention,” said Rashford.
“He keeps in contact with us and let us know where we are at.”
Rashford is undoubtedly better placed to feature in Southgate’s plans after his performance on Saturday, but his World Cup prospects may still hinge on how much he features for Mourinho in the final months of the season.
Tellingly, despite his two goals, it was Rashford and not Sanchez who was sacrificed as the Portuguese looked to shut up shop in the final 20 minutes by introducing Marouane Fellaini.
Mourinho was booed by the United fans for his decision, which he defended by citing a fear Rashford could have seen a second yellow card.
However, with Pogba soon to be back from injury, Mourinho will most likely have to make a brave decision by dropping the £89 million ($123 million) Frenchman or Sanchez if he is to continue to show faith in Rashford.