Clausura table-toppers Boca Juniors managed only a 1-1 draw with bottom club Banfield despite having a numerical advantage for all but four minutes of the match.
Victory would have left them three points ahead of Arsenal Sarandi in a tight title race but they could not assert themselves even after Rodrigo Pepe's early red card.
Indeed, Banfield took the lead in the 47th minute when Agustin Alayes notched. Three minutes later Santiago Ladino's own-goal levelled the scores.
Newell's Old Boys moved into third with a 2-1 win at home to Independiente.
The visitors went ahead through Ernesto Farias, only for goals from Pablo Perez and Victor Aquino to reverse the result.
Velez Sarsfield are six points off Boca with a game in hand after their 2-1 win over Atletico Rafaela.
Juan Manuel Martinez and Mauro Obolo scored in six second-half minutes to put Sarsfield in front, with Federico Gonzalez hauling one back for the away side.
Union Santa Fe and San Martin San Juan drew 0-0.