Boca Juniors collected a crucial away goal but couldn't keep the lead in a 1-1 draw with Uruguay's Nacional in their quarterfinal first-leg tie on Thursday.
Boca, who defeated Cerro Porteno in the round-of-16 stage of the competition, struck the home side on 70 minutes through Frank Fabra.
The galloping Colombian left-back collected a pass on the left, took two touches and fired a sliding, left-footed shot inside goalkeeper Esteban Conde's far post.
The Argentine's advantage would not last, however. The Uruguayans had their equaliser just six minutes later. From a corner, Seba Fernandez fired in an unstoppable right-footed shot past Agustin Orion to send the tie to Buenos Aires all square.
In the other game, Rosario Central scored a well-deserved 1-0 victory over Colombia's Atletico Nacional in Rosario.
The Argentines went ahead in sensational fashion on six minutes -- Walter Montoya stepping in front of a pass and wonderfully lobbing keeper Franco Armani from 35 yards out.
The hosts nearly doubled their lead but for a spectacular sequence of saves from Armani in the 62nd minute. The Atletico keeper stopped three consecutive Rosario shots -- the final two from very close range -- to improbably keep the score level ahead of the return leg in Barranquilla