Ignacio Piatti's second-half brace helped the league leaders stay top after a 2-2 draw at Atletico Rafaela.
Second-placed Newell's Old Boys drew 1-1 at home to fourth-placed Arsenal and Lanus were held 0-0 by Gimnasia La Plata.
At Atletico Rafaela's Estadio Nuevo Monumental, the hosts took an 11th-minute lead through Lucas Albertengo.
Given acres of space, Juan Eluchans whipped in a cross from the left and Albertengo headed past Sebastian Torrico.
The hosts looked headed for victory six minutes into the second half as a well-paid advantage by the referee led to Diego Vera striking into the bottom corner.
Piatti powered San Lorenzo back into the game in the 66th minute with a thunderous strike.
From 20 yards, Piatti hammered a powerful low free-kick into the roof of the net, giving Esteban Conde no chance.
The 28-year-old's second goal – on 86 minutes – came after three quality touches in the area before he finished past Conde.
Meanwhile, Newell's Old Boys were unable to hold onto their lead as Marcos Caceres' first-half goal was cancelled out by Arsenal's Mariano Echevarria.
Lucas Pratto's 85th-minute winner saw Velez Sarsfield edge Godoy Cruz 2-1 and Boca Juniors slumped to their second straight league loss in a 2-0 defeat at home to All Boys.
Argentinos Juniors and Quilmes played out a 1-1 draw and Dylan Gissi's goal was all Olimpo needed in a 1-0 win over Rosario Central.
Racing Club had enough to beat River Plate 1-0, Estudiantes were 1-0 victors at home to Colon and Belgrano claimed a 2-0 win at home to Tigre.
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