San Lorenzo drew first blood in the quarter-finals of the Copa Libertadores, while Santos and Gremio were held in their opening-leg matches.
Champions in 2014, San Lorenzo accounted for Lanus 2-0 in Wednesday's all-Argentinean clash thanks to a brace from Nicolas Blandi.
Welcoming Lanus to Estadio Pedro Bidegain, San Lorenzo took a lead into the half-time interval courtesy of Blandi.
Blandi opened the scoring in the 34th minute, weaving his way past Diego Braghieri before curling the ball beyond Lanus goalkeeper Esteban Andrada.
The 27-year-old doubled the lead six minutes into the second half, stepping up to convert his own penalty.
Con doblete de Nicolás Blandi, San Lorenzo ganó 2-0 a Lanús en la ida de los cuartos de final de la September 14, 2017
Brazilian duo Santos and Gremio, who share five Libertadores between them, drew on Wednesday.
Santos – three-time winners – left Ecuador with a draw and an away goal following their 1-1 stalemate against Barcelona.
Gremio, meanwhile, played out a scoreless draw at fellow Brazilian side Botafogo.
