RIO DE JANEIRO, April 11 (Reuters) - Brazilian champions Sao Paulo slumped to a shock 1-0 defeat away to modest Chilean side Audax Italiano in the Libertadores Cup. Renato Ramos scored in the 77th minute for Audax, who overcame the absence of their inspirational midfielder Carlos Villanueva, missing through injury, in the Group Seven match in Santiago late on Thursday. Colombian champions Atletico Nacional won 3-1 at Paraguay's Sportivo Luqueno in the same group to go top on goal difference from Sao Paulo with one match each to play. Both teams have eight points while Audax have seven and Sportivo four. Sportivo host Audax on April 23 and Atletico visit Sao Paulo. Chilean champions Colo Colo left Group Three wide open by beating UA Maracaibo of Venezuela 2-0 in Santiago with goals early in the second half from Gustavo Biscayzacu and Lucas Barrios. With one round of matches left to play, Mexico's Atlas lead with 10 points, Colo Colo have nine and defending champions Boca Juniors have seven. Boca need to beat UA Maracaibo by five goals at home in their final game on April 22 to make sure of qualifying without having to depend on the result of the Colo Colo v Atlas game the same day. However, if Atlas beat Colo Colo, a straight win will be enough for Boca.