Lanus, a modest club from the southern suburbs of the capital, went ahead in their first attack with midfielder Guido Pizarro volleying home Uruguayan Mario Regueiro's cross from the left less than half a minute after kick-off.
Substitute Diego Gonzalez raced past two challenges and beat goalkeeper Juan Carlos Olave from close range four minutes into added time to secure the points.
The side trained by former Boca Juniors and Columbus Crew forward Guillermo Barros Schelotto, in his debut season as a coach, joined Velez Sarsfield on 32 points from 16 matches.
Velez and Newell's Old Boys, three points further back, both lost on Sunday.
Boca Juniors won 1-0 at Velez for only their second victory in nine matches to climb into fourth place five points behind the leaders.
Lanus beat Tigre 4-1 eight days ago and San Martin 2-1 in midweek, both at home, as part of their seven-match streak.
"We played an almost perfect match and we took nine points in the week," Lanus goal scorer Pizarro said.
Barros Schelotto, nicknamed Mellizo (twin) with his brother Gustavo as his assistant coach, is an idol at Boca and his success at Lanus has caught the eye of directors at his former club looking to offload unpopular coach Julio Cesar Falcioni.