The midfielder set up Julian Alvarez’s opening goal in the 49th minute and played the entire Group A match in Atlanta.
After Lionel Messi threaded a pass to Mac Allister, the Canadian custodian Maxime Crepeau valiantly beat him and poked the ball into Alvarez’s path inside the penalty area.
Two minutes remaining in the ninety, Lautaro Martinez completed the scoring for Argentina.
Next up for the reigning champs is a match against Chile early on Wednesday.