Lucas Viatri headed a brilliant late winner as Boca Juniors beat leader Estudiantes 2-1 in the Argentine Clausura.
Estudiantes went ahead after six minutes when Hernan Lopez converted a deep cross from the left flank, but Juan Roman Riquelme's curling 22-yard free-kick found the top right corner for an equalizer on the 15-minute mark.
The match looked like finishing level, but Viatri netted in the 89th minute with a diving header into the bottom left of Agustin Orion's goal.
Velez Sarsfield and Argentinos Juniors were both stationed just one point behind Estudiantes before Sunday's matches, and they were joined in a four-way tie for second place on 14 points by River Plate and Godoy Cruz.
River Plate won 1-0 at Quilmes, with Paulo Ferrari's chip putting the finishing touch to a thrilling team move in the 13th minute.
Godoy Cruz were 3-1 winners at home against Huracan, with Alvaro Navarro scoring in the third and 15th minutes and Rodrigo Salinas adding a penalty in the 39th minute. Huracan had been briefly level through Javier Campora's sixth-minute effort.
San Lorenzo would have gone to the top of the table had it won its home game against Colon Santa Fe, but the visiting team departed with a 2-1 victory.
Lucas Acosta headed an early double, scoring in the 19th and 35th minutes, to put Colon Santa Fe in charge.
Cristian Ledesma was sent off after 58 minutes to hand San Lorenzo a one-man advantage, but they could only manage a last-minute goal from substitute Giancarlo Carmona.