Rolando Schiavi scored an own goal two minutes from time to condemn Clausura leaders Boca Juniors to a 2-1 defeat at Tigre on Sunday.
Boca appeared to have rescued a point when Juan Insaurralde netted in the 79th minute to cancel out Diego Morales' 27th-minute opener.
But Schiavi inadvertently intervened, allowing Newell's Old Boys to pull level on points with the leaders courtesy of a 3-0 win over Banfield.
All the goals came in the last 21 minutes, with Santiago Vergini, Fabian Munoz and Victor Aquino all scoring.
Newell's overtook Arsenal Sarandi, who slipped to a 1-0 defeat at Union Santa Fe.
Juan Cavallo scored the only goal seven minutes into the second half, while Arsenal had Jorge Ortiz sent off moments from the end.
The day's other game, between Argentinos Juniors and Belgrano Cordoba, finished 0-0, with Juan Sabia sent off for the hosts after 70 minutes.