Jadon Sancho, Fred, Anthony Martial and Facundo Pellistri were on the scoresheet against Jurgen Klopp's side, as the Red Devils made the perfect start to their pre-season.
Malacia is Man United's only signing of the summer thus far, with the Netherlands international recently making the move to Old Trafford from Feyenoord.
The defender replaced Luke Shaw at the interval of Tuesday's friendly and played the whole second half against last season's Champions League finalists.
The 22-year-old said that he was delighted to make his Man United debut and revealed that he has realised his dream of playing in the Premier League by moving to the English giants.
"I'm very happy. It feels amazing to be here, to wear this shirt and play with these people. It was difficult because of the weather, it's very hot, but we made it," Malacia told MUTV.
"Of course. It's a dream for me to play there [the Premier League] and now I'm here. [I hope to add] some good defensive [work], hope to get some assists and get some energy to the team."
Malacia will now be hoping to be given the chance to start when Man United continue their preparations for the 2022-23 campaign with a clash against Melbourne Victory on July 15.
The 20-time English champions will then take on Crystal Palace and Aston Villa, with both fixtures also taking place in Australia, before returning to Europe for friendlies against Atletico Madrid and Rayo Vallecano.
Malacia is expected to provide competition for Shaw at left-back next season, with Alex Telles potentially being allowed to leave the club before the end of the summer transfer window.
When recently questioned on the defender, Red Devils boss Erik ten Hag branded him "the modern left-back" and tipped the Dutchman to enjoy a successful career at the club.
"I think he's the modern left-back or full-back," he told MUTV. "He suits the profile [we were looking for] and most important from every full-back is that he closes the right area.
"He can also take part in the offensive side of our game, and he can do that really well. I think he will really contribute to the team."
Malacia, who is believed to have cost Man United in the region of £13m, contributed four goals and 10 assists in his 136 appearances for Feyenoord's first team during his time at the club.
Meanwhile, he enjoyed a productive 2021-22 season, featuring on 50 occasions for De Stadionclub, contributing one goal and five assists in the process.