The 18-year-old Scotland youth international slotted into a new position as a left-sided centre-back for Monday evening's Premier League 2 clash at Stevenage FC.
He was named alongside first-team regulars Adam Lallana, Danny Ings, Dominic Solanke and Ben Woodburn in a strong starting line-up for Neil Critchley's team.
But the young Reds ended the game with a disappointing result and just nine men as Lallana was shown a straight red card and George Johnston was also dismissed for two bookable offences.
On a personal level, however, Gallacher could take consolation from making a first appearance since joining the club from Falkirk last month.
He told Liverpoolfc.com: “To get my first start so soon and playing in a game of such high intensity, I really enjoyed it.
“It was an unbelievable game, end to end, very quick with both teams pressing and you didn’t have a lot of time on the ball.
“The pitch wasn’t the greatest but the game was high intensity and there was good quality going forward.
“Both teams defended well. Us going down to nine men didn’t help but the boys didn’t stop, we didn’t give up, we kept going at it and they were hanging on towards the end.
“This is a young group of players and sometimes you would expect heads to go down because there’s not that much experience but the boys stuck to it and we battled away.”
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Gallacher also revealed he is adapting quickly to his new surroundings on Merseyside after moving from Scotland.
“It’s really good and I’m settling in very well,” he added.
“The boys are great and the coaching staff are all really helpful and I’m enjoying it so far.”