Liverpool sealed their place in the fourth round of the competition after an own goal and Luis Diaz strike in the last 10 minutes saw off the Gunners, who had put pressure on throughout the contest.
Alexander-Arnold once again moved into midfield following the introduction of Conor Bradley in the second half, and it was his free-kick that forced Jakub Kiwior to head home at the expense of his team to give the Reds the lead.
Speaking after the game, the vice-captain hailed the “impact” of the manager’s half-time tweaks in enabling the side to get a foothold in the encounter.
“It’s huge. We’ve got a lot of players missing today with the lads on internationals and Virg not in the squad. We dug deep with two late goals,” Liverpool’s No. 66 told BBC Sport after the game.
“We changed things around at half-time and we came out and played football, created our chances. The change of system made an impact for us.
“At times in the first half we were a bit naïve playing out from the back. We stuck with how we play.
“We have our identity and used the speed of Darwin and Lucho [Luis Diaz]. Darwin went out wide and used his speed against their full-back.”
Alexander-Arnold’s late free-kick gave the Gunners all sorts of problems, with the own goal allowing the Reds to break the deadlock in what had been a lively, albeit goalless encounter to that point.
He explained the intention behind his set piece, detailing that he wanted to make it “as hard as possible” for the hosts to rid themselves of danger.
The right-back continued: “With the in swinger you want to hit it as well as possible. You want to make it as hard as possible for them to clear. We hit the woodwork a couple of times.”
Along with a place in the hat for the next stage, the win lays down a significant marker against a team likely to jostle for the Premier League title between now and May.
There were several impressive individual performances, but Alexander-Arnold once again outlined his importance to this Liverpool team, while wearing the captain’s armband in Virgil van Dijk‘s absence.