Boca Juniors lost ground on Argentinian Clausura leaders Newell's Old Boys when they were held to a goalless home draw by Velez Sarsfield on Sunday.
With Newell's having moved three points clear at the summit on Saturday night thanks to a 3-1 victory over Union Santa Fe, Julio Cesar Falcioni's side were looking to respond but could find no way through the Velez defence.
The hosts' cause was not helped by the dismissal of Facundo Roncaglia four minutes before half-time. The visitors could not capitalise on their man advantage, but moved up a place to sixth with their point.
Third-placed Tigre were also held to a draw, 1-1 at Colon Santa Fe, after playing for three quarters of the match a man down.
Carlos Luna secured the point with a 13th-minute leveller after Sebastian Prediger had put Colon ahead in the first minute. Tigre defender Lucas Orban saw red in the 22nd minute but there were no further goals.
Elsewhere, Jose Morales netted an 89th-minute winner as Argentinos Juniors edged Racing Club 2-1 to climb to ninth.
The game looked to be heading for a draw after Juan Ramirez's early opener for Argentinos was swiftly cancelled out by Valentin Viola, but Morales had other ideas. The hosts had Sergio Escudero sent off in the dying seconds but there was no time for Racing to find an equaliser.
Finally, early goals from Diego Braghieri and Mariano Pavone earned Lanus a 2-0 triumph over Banfield, Facundo Ferreira's late effort proving scant consolation for the second-bottom visitors.