Chilean side Cobreloa claimed a crucial 1-0 win away to Tacuary in the first leg of the Copa Sudamericana first round.
Patricio Troncoso netted the winning goal 12 minutes before the final whistle when he scored with a long-distance shot to help Javier Torrente's side claim the win at the Estadio Roberto Bettega in Asuncion.
The away goal could prove crucial in the second leg in Calama on August 7.
Troncoso told Fox Sports: "It was a very complicated game, but fortunately we managed to make it. We are now a little bit relaxed ahead of the second leg, but we must be careful anyway. We must keep this attitude."
In Montevideo, Uruguay's Danubio played out a goalless draw with Paraguayan giants Olimpia. Daniel Sanchez's Danubio had three chances to win the match but his the post on each occasion.
Midfielder Matias Melazzi was the first to hit the post in the 23rd minute, while a header by Fabricio Formiliano from a free-kick also hit the frame of the goal seven minutes before half-time.
Richard Nunez also beat Olimpia keeper Martin Silva but was denied by the post meaning neither side has the advantage ahead of the return in a fortnight in Asuncion.