A 10-man Gremio beat Libertad 2-0 in the first leg of their Copa Libertadores last-16 tie on Thursday.
Diego Tardelli's fine second-half volley and David Braz's header saw the Brazilian outfit edge to victory at the Arena do Gremio.
It came despite being reduced to 10 men in the 51st minute, when Pedro Geromel was sent off for a rash studs-up challenge on Edgar Benitez.
However, Gremio still found the opener 20 minutes later through substitute Tardelli.
A corner from the right was flicked on before Tardelli volleyed in expertly from close range.
Gremio took control of the tie with six minutes remaining, Braz heading in a set-piece from Alisson to put his side in command ahead of next week's second leg.