Sao Paulo drew first blood in the opening leg of their Copa Libertadores quarter-final against Brazilian rivals Atletico Mineiro with a scrappy 1-0 win.

A header from substitute Michel Bastos with 11 minutes remaining was all that separated the two teams in a clash blighted by constant fouling on Wednesday.

A total of 10 yellow cards were dished out by referee Wilmar Roldan, with seven handed out by half-time alone at Estadio do Morumbi, as both sides struggled to generate any real rhythm and momentum.

But just as the match was petering out for a draw, former Brazil international Bastos came off the bench and glanced a header beyond Mineiro goalkeeper Victor within 16 minutes of his introduction.

Bastos' header sparked jubilation among the Sao Paulo faithful but also worrying scenes after some fans fell from the stands as a fence made way, with one young supporter attended to by two Sao Paulo players amid the celebrations.

When play finally resumed, Mineiro - who played the entire second half without Robinho after the former AC Milan and Real Madrid star was carted off the pitch due to injury in the 39th minute - were unable to score an equaliser.

Mineiro will host the return leg on May 18.