Argentine championship leaders San Lorenzo slumped to a shock 2-1 defeat away to Velez Sarsfield on Saturday evening, only their second loss in second outings.
The Cyclone stayed top of the Clausura championship with 31 points, four ahead of Boca Juniors who are away to Argentinos Juniors on Sunday.
Velez, who have suffered from inconsistent form under Ricardo La Volpe and on Friday suspended goalkeeper Gaston Sessa for indiscipline, went ahead with a Gustavo Balvorin header in the 58th minute.
Mauro Zarate increased their lead nine minutes later when he scored direct from a free kick and Cristian Tula pulled one back for San Lorenzo with 18 minutes to play.
Racing Club, who have won only twice, continued to struggle as they were held 1-1 at home by Banfield.
Gustavo Cabral headed Racing in front from a free kick in the 18th minute but turned villain when he handled the ball and gave away a penalty in the 32nd minute.
Banfield goalkeeper Christian Lucchetti converted for his second goal of the competition.
