River Plate came from behind against South American champion San Lorenzo to move top of the Argentine Primera Division.
Goals from Leonardo Pisculichi, Teofilo Gutierrez and Lucas Boye cancelled out Mauro Matos' opener as River prevailed 3-1 against the Copa Libertadores title holders on Monday (AEST).
San Lorenzo's woes were compounded after it was forced to play the final 12 minutes a man down - and was down to nine with four minutes remaining - as Juan Mercier and Mauro Cetto were sent off at the Estadio Pedro Bidegain.
River opened up a one-point lead atop the summit with 13 points from five matches after Velez Sarsfield's perfect start to the season came to an end as it lost 3-1 at Boca Juniors.
San Lorenzo - second from bottom in the table - made a dream start to proceedings in front of its own fans when Matos opened the scoring after six minutes.
River was caught on the break as Hector Villalba squared the ball to an unmarked Matos inside the penalty area and the veteran striker made no mistake from close range.
The home side was pegged back just six minutes later following Pisculichi's half-volley from outside the box.
It got better for River after half-time as it added two unanswered goals through Gutierrez and Boye.
Colombian attacker Gutierrez made it four goals in three games when he tapped the ball home from inside the goal area a minute shy of the hour-mark.
One minute after Mercier was shown a straight red card, Boye headed home to double the visitor's advantage.
To make matters worse for San Lorenzo, Cetto was shown a second yellow card with four minutes remaining.
It was an identical scoreline at the Estadio Alberto Jacinto Armando - commonly known as La Bombonera - on Tuesday (AEST) as Boca made a winning start under new coach Rodolfo Arruabarrena.
Arruabarrena - winner of four trophies with the club during his playing days - was appointed after Carlos Bianchi was sacked on Thursday and it appeared to work wonders as it defeated Velez courtesy of second-half goals from Daniel Diaz, Cesar Meli and Andres Chavez.
Velez's slip up opened the door for Newell's Old Boys, who closed to within a point of second spot thanks to a 1-0 win at home to Estudiantes on Sunday (AEST).
Mauricio Tevez's 71st-minute strike proved the difference as Newell's preserved its unbeaten start to the season.
In other results, fourth-placed Rosario Central accounted for lowly Defensa y Justicia 3-1.
Rosario is level on nine points with Arsenal, Independiente and Racing Club.
Arsenal edged 10-man Banfield 1-0, while Independiente upstaged Racing 2-1 with all three goals scored during the first-half.
Belgrano notched its first win of the season, routing Atletico Rafaela 3-0.
Gimnasia La Plata was also a winner for the first time after Jorge Rojas and Javier Mendoza inspired it to a 2-0 victory over Godoy Cruz.
Meanwhile, Tigres and basement club Quilmes played out a goalless draw.