Arsenal Sarandi claimed the narrowest of advantages heading into the final week of the season as they earned a 3-0 win at fellow Clausura title challengers Boca Juniors.
Emilio Zelaya opened the scoring in just the second minute, before Luciano Leguizamon netted either side of half-time to give Arsenal a comfortable cushion.
Boca, who had led the table for much of the season, had Franco Sosa sent off in the 85th minute.
Heading into the final round of matches Arsenal sit top, level on points and goal difference with Tigre and leading only on goals scored.
Copa Libertadores semi-finalists Boca, going for the treble, are two points back of their two rivals.
On Saturday, Arsenal host Belgrano Cordoba, Tigre entertain Independiente and Boca go to All Boys.
Elsewhere on Sunday Cesar Carignano scored twice to lead Atletico Rafaela to a 4-2 win over Racing Club. Carignano netted from the spot after 37 minutes but Atletico found themselves 2-1 down thanks to goals either side of half-time from Bruno Zuculini and Lucas Castroman.
Alexis Castro levelled just a minute later though, before goals from Carignano and Federico Gonzalez sealed the points.
Argentinos Juniors beat All Boys 1-0 in a match which ended up nine v seven. Jonathan Ferrari was first to go for All Boys in the 16th minute, before Juan Rodriguez joined his team-mate in the 50th minute, along with German Basualdo for the hosts.
Juniors' 10 men netted through Juan Jose Morales in the 74th minute, but he was sent off to even up the sides two minutes later - before All Boys lost two more, Maximiliano Coronel (80) and Mauro Matos.
The day's other game, between Independiente and San Lorenzo, was goalless. Independiente had Julian Velazquez sent off in the 49th minute.