Olimpo missed the chance to climb into the top three in the Clausura as they were held to a 2-2 draw at home by Tigre.
The home side led through Diego Galvan's seventh-minute strike, but goals after 33 and 50 minutes from Roman Martinez turned the match in Tigre's favour.
Nestor Bareiro got Olimpo back on level terms six minutes later, but they were unable to add to their total.
Lanus moved level on points with Olimpo with a 1-0 victory at Colon Santa Fe.
A Leandro Diaz effort after 56 minutes was enough to separate the two teams, although Lanus' win was soured slightly by the last-minute dismissal of Paolo Goltz.
Boca Juniors disappointing campaign continued with a 1-1 draw against Independiente.
Despite going ahead with Martin Palermo's 22nd-minute goal, the hosts were pegged back by an equaliser from substitute Lucas Villafanez 13 minutes from time.
Boca lie 14th, nine points behind leaders Velez Sarsfield.