Argentine championship leaders Lanus slumped to a 2-1 defeat away to bottom-of-the-table Argentinos Juniors on Friday.
Argentinos, who claimed their first win of the Clausura tournament, went ahead after 10 minutes at the Diego Armando Maradona stadium when Ignacio Canuto headed in from a corner.
The hosts dominated the game but Lanus equalised a minute before halftime when Diego Lagos volleyed home from 15 metres.
Gabriel Hauche scored the winner three minutes after the re-start, firing his shot under Carlos Bossio after Carlos Quintana failed to clear the ball.
Lanus have 18 points from nine games, one ahead of Colon who host Arsenal on Saturday, and two more than Velez Sarsfield, away to San Lorenzo on Sunday.
The win lifted Argentinos off the bottom of the 20-team table with eight points from nine games.