Boca Juniors were held to a 0-0 draw by Santos in the first leg of their Copa Libertadores semi-final on Wednesday.
Neither team was able to find a breakthrough in a cagey clash at La Bombonera.
The goalless draw, in which there were just four shots on target, leaves the tie wide open ahead of the return leg in Santos on January 13.
Sebastian Villa hit the crossbar for six-time champions Boca in the eighth minute, although the forward was offside.
Both teams pushed for a goal but struggled to create much of note.
Santos, who last reached the Libertadores final in 2011, had a late penalty shout turned down after Marinho appeared to be brought down by Carlos Izquierdoz.