Denis Stracqualursi scored in 73rd minute Saturday, lifting 10-man Tigre to a 2-1 victory over Argentina Apertura leaders Estudiantes.
Estudiantes remained atop the standings on 30 points but missed the chance to move six points clear of second-place Velez.
Diego Morales gave Tigre a 1-0 lead in the 24th minute, before teammate Roman Martinez was sent off just after halftime. Estudiantes were soon back on level terms with Leonardo Benitez equalizing in the 51st minute from a soaring left-foot volley. The victory moves Tigre to 18 points.
In Saturday's other match, third-place Arsenal drew 0-0 with All Boys. On Friday, Colon defeated Huracan 2-1 and Banfield played a 0-0 draw with Gimnasia. Arsenal has 25 points in third place.
Velez faces Lanus Sunday and could move level on points with a victory.
Tigre's victory was its most important of the season with fans singing and waving banners near the end of the match.
On Friday in Colon's victory, Joaquin Larrivey scored in the 33rd and Marcelo Goux got the winner with a header five minutes from full-time.
Boca Juniors and River Plate square off on Tuesday in what is traditionally the biggest match of the season. However, this time it could be a dud.
River Plate is winless in seven games, prompting the firing this week of coach Angel Cappa. Boca coach Claudio Borghi has also talked about quitting in the midst of a poor season.
In another blow for Boca, playmaker Juan Roman Riquelme injured his right foot in practice on Friday and is doubtful. The former Barcelona and Villareal star played his first match last weekend after missing six months following surgery on his left knee.
