Tigre extended Newell's Old Boys' winless streak to five games with a 2-1 victory on Monday, which allowed San Lorenzo to stay top of the table following their 4-2 victory over Belgrano.
Juan Antonio Pizzi's San Lorenzo team moved to 30 points from 16 rounds, while Newell's remain on 29 after three draws and two defeats in their past five matches.
With three rounds remaining in the Argentine Torneo Inicial, Lanus (28 points) claimed their fifth straight victory to stay within two points of San Lorenzo in third, while Arsenal are also on 28 points in fourth.
At San Lorenzo's Estadio Pedro Bidegain, the home side took the lead in just the third minute thanks to Emanuel Mas' thunderous strike into the roof of the net.
It was 2-0 in the 10th minute when Ignacio Piatti cut the ball back for Angel Correa to finish through the legs of Belgrano goalkeeper Juan Olave but the visitors hit back just before the half-hour mark through Cesar Pereyra.
Belgrano drew level in the 60th minute when San Lorenzo's Pablo Alvarado put the ball into his own net but three minutes later the hosts were ahead again when Piatti won and converted a penalty.
San Lorenzo wrapped up their win on Saturday, and took a step towards the Torneo Inicial title, when Mauro Cetto volleyed home Leandro Romagnoli's 72nd-minute corner.
Tigre stunned Newell's on Monday after initially trailing the reigning Torneo Final champions.
Fabian Munoz put Newell's in front in the 20th minute but Tigre were level at half-time following Sebastian Rusculleda's strike 10 minutes before the break.
A penalty to Angel Diaz in the 64th minute saw Tigre win and move up to 14th on the Primera Division table.
Lanus had to come from two goals adrift to continue their winning streak, overcoming All Boys 3-2, while Arsenal held on to triumph by the same scoreline against Boca Juniors.
In other results, Olimpo won 3-1 away to River Plate, Velez Sarsfield defeated Rosario Central 3-2, Quilmes drew 1-1 with Racing Club, Godoy Cruz prevailed 2-1 against Estudiantes and Gimnasia La Plata held Argentinos Juniors to a scoreless draw.
The clash between Colon and Atletico Rafaela was postponed.
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