Boca Juniors and Buenos Aires city rival River Plate both lost ground at the top of Argentina's first division on Sunday, with Boca losing 2-0 to Estudiantes and River going down 2-1 to Colon.
Boca Juniors is now in 10th place in the standings with River in in 14th, while Argentinos Juniors takes first place after the fourth round following a 1-0 victory over Tigre on Saturday.
In other Sunday's other game, Olimpo drew 1-1 with All Boys. On Saturday, Velez Sarsfield and Lanus drew 0-0 and Rosario defeated Godoy Cruz 1-0 thanks to an 85th minute goal from the penalty spot from Sebastian Abreu. In Friday's games, Gimnasia won 2-1 against Belgrano, Newell's Old Boys defeated Rafaela 2-0 and Arsenal overcame Racing 2-0.
Guido Carrillo scored both goals for Estudiantes, rifling a first-time shot into the net from the edge of the area for the first in the 55th. He added his second in second half injury time from the penalty spot after a hard-fought game.
River Plate newcomer and Colombia international Teofilo Gutierrez scored a late 87th minute goal from close range, but it was too late for the Buenos Aires club to get an equalizer.
Colon took the lead in the 52nd after a string of defensive errors from River left Gaston Curuchet free at the back post to smash the ball into the roof of the net from two yards (meters) out.
Ruben Ramirez volleyed in the second for Colon in the 78th, steering his shot into the far corner after River failed to clear a free-kick swung in from the left.
Argentinos Juniors' substitute Daniel Villalva scored the lone goal of the game against Tigre in the 77th, stealing the ball in front of defender Ignacio Fideleff and finishing with ease.
On Monday, Quilmes play San Lorenzo in the remaining game of the fourth round.