Santos leapfrogged Estudiantes as it continued its winning run in the Copa Libertadores, while River Plate played out another draw.
Arthur Gomes was the hero for Santos, which moved top of Group Six with a 1-0 victory at Estudiantes.
It was not the cleanest of goals but Gomes was on hand to bundle the ball over on the goal line after Eduardo Sasha's effort hit the post in Buenos Aires.
The win saw Santos moved two points ahead of its Argentine rival in the group standings.
River is still searching for its first win of the campaign after a goalless draw against Santa Fe in Group Four.
Delfin won for the first time in three games, accounting for Colo-Colo 2-0 in Group Two, while leader Atletico Nacional lost away to Bolivar.