Velez, winners of the "Inicial" championship in December, beat Argentinos Juniors 1-0 at the Diego Armando Maradona stadium through a fine strike from 30 metres by Lucas Pratto.
Argentinos had started strongly but a power failure after 12 minutes caused a delay of more than half an hour and on their return to action Velez had adjusted their tactical plans and took control.
The bad news for Velez, who are eyeing a second South American Libertadores Cup this year, was the loss with a serious ankle injury of Pratto's strike partner Facundo Ferreyra, joint top scorer of the "Inicial" with 13 goals.
The lights also failed at the "15 de abril" stadium in Santa Fe, where Union and Arsenal drew 1-1, causing a 20-minute delay in the second half.
Arsenal winger Pablo Luguercio earned the first red card of the championship for reacting with a slap in the face for Emanuel Britez after the Union defender had touched his buttocks as he was shielding the ball.
Boca Juniors, with coach Carlos Bianchi back on the bench again a decade after ending his previous spell at the club, are at home to Quilmes in La Bombonera on Saturday.
Their arch-rivals River Plate visit Belgrano in Cordoba on Sunday.
- Sports & Recreation
- Argentinos Juniors
- Diego Armando Maradona