Banfield's dismal Apertura campaign continued as they were beaten 2-1 by mid-table San Martin San Juan.
Gaston Caprari opened the scoring in the 11th minute before Sebastian Penco doubled the home side's advantage from the penalty spot seven minutes before half-time.
Although Jonathan Gomez pulled a goal back three minutes from the end, it could not prevent Banfield slipping to the bottom of the table.
Estudiantes moved off the foot with a goalless draw against third-placed Racing Club, whose unbeaten record remains after a ninth draw in 13 games.
Rodrigo was dismissed for the home side after half an hour but the numbers were evened up nine minutes from time when Lucas Aveldano saw red.
Union Santa Fe and Tigre drew 1-1. Javier Carrasco gave the visitors the lead with 21 minutes to go but Juan Avendano levelled for Union four minutes later, before Tigre had Roman Martinez sent off four minutes from time.
