The Reds are facing Toulouse in the Europa League with goals from Diogo Jota, Wataru Endo, Darwin Nunez and Ryan Gravenberch putting them 4-1 up at Anfield.
Despite that, the French side were still causing plenty of problems, with Liverpool's backline feeling the pressure as a result.
Caoimhin Kelleher picked up the ball in his own six-yard box and tried to play the ball out, however he scuffed his kick to put Liverpool under immediate pressure.
Picked up by the attacker, the ball was squared to Gabriel Suazo who had the simple task of slamming the ball home, but Alexander-Arnold had other ideas.
The attack-minded full-back managed to get himself back in position on the goal line, before blocking the effort of Suazo to spare Kelleher's blushes and maintain Liverpool's two-goal lead.
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Alexander-Arnold's defensive contribution is often questioned when compared to his attacking output which is sublime for a defender.
However on this occasion he's showed exactly why Jurgen Klopp has kept the faith with him in his back line for so long.
Following the goal-saving challenge, Liverpool went on to secure the result that they wanted.
Gravenberch made it 4-1 as he struck home with his left foot on the rebound after Nunez inexplicably hit the post with an open goal gaping, before Mohamed Salah made it five late on.
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That result means that it's three wins from three for the Reds, putting them in a very strong position to progress to the next round.