Two goals from Nicolas Blandi helped Boca Juniors beat their arch-rivals River Plate 2-0 in a typically heated pre-season clash in Resistencia.
The Buenos Aires clubs will not meet in the top flight this season after River's relegation to Nacional B but they provided plenty of fireworks in northern Argentina.
In front of 25,000 fans - and 2,500 local and national police - Boca took the lead in the seventh minute when Blandi headed home Pablo Mouche's cross.
River's hopes clawing themselves back into the match were dented after half an hour when Alejandro Dominguez was shown a second yellow card for dissent.
But the Nacional B side kept the score at 1-0 and were on a level playing field midway through the second half when Boca's Facundo Roncaglia was sent off.
Although David Trezeguet came off the bench he could not equalise for River and Blandi sealed victory with just over 10 minutes left.
The two sides meet again in Mendoza on Sunday.