The winger continued his fine form this season by firing a controlled, sidefoot volley into the top corner from Angel Di Maria's cross to make it 2-0 on 40 minutes.
Di Maria was involved in all four goals, scoring the fourth, as Argentina raced into a 4-0 lead before Germany's consolation efforts. Sergio Aguero and Federico Fernandez also scored for Argentina with Andre Schurrle and Mario Gotze replying for the world champions.
Erik played for 68 minutes before being replaced by Fernando Gago.
Elsewhere, Christian Eriksen played the first half as Denmark were beaten 2-1 by Turkey in a friendly in Odense.
Danny Rose and Andros Townsend were unused substitutes as England beat Norway 1-0 in a friendly at Wembley, Wayne Rooney converting a penalty for the only goal of the game.
Josh Onomah was a late substitute as England Under-18s beat Holland 4-1 at Leigh Sports Village.
The friendly action continues on Thursday night with Nacer Chadli, Mousa Dembele and Jan Vertonghen in the Belgium squad to face Australia and Hugo Lloris expected to captain France against Spain.
Meanwhile, Jordan Archer, currently on loan at Northampton Town, is with the Scotland U21 squad for their European U21 qualifier against Slovakia.