Marcelo Delgado scored two spectacular goals to help Boca Juniors win 2-1at arch-rivals River Plate.
Boca, who won for the first time in five years at the ground of their most bitter rivals, went ahead when Delgado curled in a-free kick three minutes before half time.
River hit back after the break when substitute Esteban Fuertes scored from close range. But Delgado struck again with 15 minutes left, controlling the ball on his chest and scoring with a rifling half-volley from 30 yards.
Police fired teargas into the crowd when River supporters tried to force their way out of the stadium after being kept inside for more than an hour following the final whistle.