Emilio Zelaya got an early goal and Juan Pablo Caffa added a second-half penalty as Arsenal won 2-0 at home against San Martin in the Argentine Apertura tournament on Monday.
Zelaya scored in the fourth minute with a close-range finish lifted over goalkeeper Luciano Pocrnjic before Caffa extended the lead with a spot kick in the 52nd.
Sebastian Penco missed a chance to cut the deficit for San Martin when he blasted a 74th-minute penalty over the bar.
The result moved Arsenal to 20 points from 14 games in mid-table, while San Martin remained in the bottom half with 15.
Boca Juniors leads the standings with 32 points, eight ahead of closest challenger Racing Club with five games left to play.