Second-half goals from Gabriel Mercado and Rodrigo Mora saw River Plate beat Paraguay's Guarani 2-0 in the first leg of their Copa Libertadores semifinal in Buenos Aires.
Mercado opened the scoring for River Plate on the hour mark and Mora doubled their advantage 13 minutes later to give the Argentinian side a promising lead ahead of next week's second leg.
River Plate travel to Asuncion next Tuesday in search of a place in the final where they could meet either Brazilian side Internacional or Mexican outfit Tigres.
Two-time Copa Libertadores champions River Plate struggled to contain Guarani in the first half at the Estadio Monumental and could have gone into the halftime interval behind after a series of defensive lapses.
Thankfully for the Argentinian side Guarani could not take advantage and the hosts claimed victory.
River Plate manager Marcelo Gallardo said: "It was a very tough, hard-to-pass match with Guarani playing well-ordered (football).
"In the second half we played more aggressively and kept trying after the first goal.
"It was a very good win for us because we scored two goals and did not concede one. We are on the right path.''