Arsenal's trip to the Estadio Ciudad de Lanus was looking like a fruitful one with 10 minutes to play, as they had their eyes on a valuable away point to boost their title chances.
However, the effect of Arsenal defender Hugo Nervo's dismissal on 64 minutes was felt late on, as Nicolas Pasquini and Santiago Silva both found the back of the net to send Lanus within four points of league leaders Newell's Old Boys.
Pasquini's 83rd-minute goal was followed by Silva's on-target shot three minutes later.
Lanus's fourth straight win sees them to 25 points, with Arsenal fifth only on goal difference.
Earlier in the weekend, top two sides Newell's and San Lorenzo played out a 1-1 draw to blow open the race for the Torneo Inicial title - with four matches to play in the season.
The hosts at the Estadio Marcelo Alberto Bielsa in Rosario led on 25 minutes when David Trezeguet struck, only for Ignacio Piatti to equalise for San Lorenzo five minutes later to keep the league leaders within reach.
San Lorenzo are two points behind Newell's in second, while Boca Juniors are third - level on 27 points with San Lorenzo - after a stunning late show to beat Tigre 2-1.
Tigre had their eyes on all three points from their trip to the Estadio Alberto Jacinto Armando in Buenos Aires, after a Claudio Perez own goal in the 18th minute gifted them the lead.
However, the visitors lost attacker Matias Perez Garcia to a red card eight minutes after the interval, and despite keeping out Boca for the most part, the dam wall broke in the final stages.
Leandro Paredes equalised on 85 minutes, before Daniel Diaz struck in the second minute of injury time to give Boca hope of titles in consecutive years after their Apertura success in 2012.
Atletico Rafaela chalked up their first league win in four matches, with a 3-1 result at home to Godoy Cruz.
A Diego Vera brace consolidated Diego Ferreira's opener for Rafaela, with the win taking them to 24 points.
Estudiantes are one point behind fifth-placed Rafaela in sixth, after a 1-1 draw at home to Rosario Central (ninth).
Rosario led on 51 minutes via a Paulo Ferrari goal but the points were split after defender Alejandro Donatti got the final touch into his own net seven minutes later.
Argentinos Juniors continued their stellar form, making it three wins from their past four with a 1-0 win away at Racing Club.
Hernan Boyero was the hero for Juniors, as they moved to 23 points and eighth spot on the table.
In other results, Quilmes had a 1-0 win away to Olimpo, All Boys were too good for Gimnasia La Plata 2-1, Belgrano's Cesar Pereyra scored both goals in his side's 2-0 win over Colon, while River Plate's trip to Velez Sarsfield ended 0-0.
