The teenager put a couple of difficult recent displays behind him to completely shackle Leroy Sane in the first leg at Anfield, earning a Man of the Match award.
And at the Etihad on Tuesday he faced a similarly tough night, but was again near-faultless, an impressive feat considering how much emphasis City put on getting Sane isolated against him.
Alexander-Arnold received recognition after the match, with Steven Gerrard singling him out for praise.
“Look at his age, the magnitude of the game over both legs, who he was up against,” Gerrard told BT Sport.
The former Reds skipper also noted the trust that Jurgen Klopp placed in the 19-year-old to play in such a game, particularly after Alexander-Arnold picked up an early yellow card.
“He has to be the star man over two legs.
“To be fair to the kid he stood up so well…The manager’s confidence in him to keep him on with a yellow card speaks volumes of their relationship.”
Rio Ferdinand also highlighted the technical strengths the No. 66 showed in both halves of the pitch.
“One vs. one especially he was brave, on the front foot defending against a super talent in Sane, he looked so comfortable,” he explained.
“Not only defensively was he fantastic but when he had the ball his distribution into front areas, finding a team-mate, was superb for a young boy.”
There were also the first murmurings of an England call-up for the teenager, who trained with the seniors in the last international break, and Frank Lampard feels he has a chance of gatecrashing the squad.
“He’s timing his run [of form] brilliantly. His calmness on the ball, we’re trying to play out from the back with England and the boy’s so comfortable on the ball,” he enthused.
“He has a massive game ahead of him to show it again and again and if he does it at this level, why not?”