Lionel Messi scored on his return from international retirement as Argentina beat Uruguay 1-0 to go top of the South American World Cup qualifying group.
Brazil remain in fifth place, outside the automatic qualification spots, despite their 3-0 win over Ecuador.
Manchester City's summer signing Gabriel Jesus, 19, scored twice on his debut. with Neymar netting the opener.
Brazil have never failed to qualify for a World Cup and are only two points behind Argentina with more than half of the qualifying campaign to go.
A top-four finish would secure automatic qualification for Russia 2018, with fifth place securing a two-legged play-off with a team from Oceania - either New Zealand, New Caledonia, Fiji, Papua New Guinea, Solomon Islands and Tahiti.
Ecuador's defeat saw them slip from second to fourth following Colombia's 2-0 victory over Venezuela - with Real Madrid's James Rodriguez scoring the first and assisting in the second for Los Cafeteros.
Peru, the 2015 Copa America semi-finalists, are eighth of nine teams and have only one victory from seven qualifying matches after losing 2-0 away to Bolivia.
In the night's other match, Paraguay beat Chile 2-1 and moved above them into sixth, four points behind Argentina.