Racing club took advantage of a goal from their keeper and an indisciplined display from San Lorenzo to secure a 4-0 win which took them second in the table.
Goalkeeper Sebastian Saja opened the scoring from the penalty spot against his old club and Javier Campora netted the third in the 63rd minute, but it was two own goals, from Santiago Gentiletti (50) and Gonzalo Prosperi (78), and two red cards which did much of the damage.
Gentiletti completed a miserable day by seeing red in the 65th minute and Abel Masuero followed suit three minutes later.
Cesar Carignano scored a hat-trick as Atletico Rafaela came away from a sea-saw game against Argentinos Juniors with a 5-3 win.
Carignano's first two, including a seventh-minute penalty, sandwiched a strike from Gaspar Iniguez and sent Atletico into the break 2-1 up.
Goals from Marcos Figueroa and Juan Luis Anangono within 10 minutes of the restart put the visitors 3-2 ahead, but two strikes from Fabricio Fontanini (58, 70) and Carignano's third five minutes later ensured Atletico took the points.
Ivan Borghello's 29th-minute strike and Angel Vildozo's penalty after 65 minutes saw All Boys come from behind to beat Lanus 2-1.
Victor Ayala (26) had opened the scoring for Lanus, who also had Maximiliano Velazquez sent off moments before the hosts' second.
In the day's other game, Mauro Obolo's goal in the 67th minute gave Godoy Cruz a 1-0 win over Estudiantes.