The Academy graduate was up against a familiar face in Ben Woodburn during the U19 European Championship qualifier in Bangor.
Woodburn won a penalty to help his country take the lead in the first half, Nathan Broadhead converting, and they doubled their advantage on the hour mark through Mark Harris.
But a deflected shot and penalty from Alexander-Arnold – who made his senior Liverpool debut against Tottenham Hotspur at Anfield last month – hauled England level within 12 minutes.
It was not enough for the Young Lions, however, as Wales produced an immediate winner, with Broadhead grabbing the decisive goal.