Monday's victory pushed Defensa y Justicia's point total to 18, leaving the club just five points back of league leader Racing Club, reports Efe.
Defensa y Justicia and Atletico Tucuman are the only undefeated teams in the tournament.
Defensa dominated San Martin during the match, but it took a late goal to secure the win.
The goal was scored by Marcelo Larrondo, who took the field in the 89th minute.
The Buenos Aires-based club will play Colombia's Junior de Barranquilla on Thursday in the Copa Sudamericana quarterfinals.
Junior won the first leg of the series 2-0 in Colombia.
San Martin de San Juan is in 22nd place, with eight points, and is one spot away from the relegation zone.
In the early match on Monday, Newell's Old Boys defeated bottom-dweller Argentinos Juniors 2-0 in a duel between teams that are trying to avoid falling into the Second Division.
As far as the standings go, Racing Club is in first place, with 23 points, followed by Atletico Tucuman, which is four points back.
Defensa y Justicia is in third place, on goal differential, with 18 points, while Union sits in fourth place, also with 18 points.
Huracan is in fifth place, on goal differential, with 17 points.
In the 11th round of play, Belgrano battles Gimnasia and Union takes on Patronato on Friday.
On Saturday, Rosario Central plays Colon; Godoy Cruz clashes with Atletico Tucuman; Estudiantes plays River Plate; and Boca Juniors takes on Tigre.
Argentinos Juniors plays Independiente; Aldosivi battles Banfield; San Lorenzo takes on Talleres; Racing Club plays Newell's Old Boys; and San Martin de Tucuman clashes with San Martin de San Juan on Sunday.
On November 5, Defensa y Justicia plays Velez Sarsfield and Lanus takes on Huracan.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
