Reigning Copa Libertadores champions Santos lost 2-1 at Bolivia's Bolivar in the first leg of their round-of-16 tie.
Santos found it difficult to play at 3,600 metres above sea level in La Paz and fell behind in unfortunate circumstances in the first minute of the game.
Jhasmani Campos' powerful free-kick hit the post and then the back of Santos goalkeeper Rafael before bouncing into the net.
Maranhao equalised in the 34th minute after Marcos Arguello saved an Elano free-kick, but Campos gave his team victory in the 74th minute with an impressive long-range free-kick.
The second leg will be played next Thursday in Brazil and Campos told Fox Sports the Bolivian side hoped for a bigger margin to take into it.
He said: "The intention was to score at least three goals or more. We were looking to beat Santos here because we know they do not like playing here. Winning is what matters, but we played great rivals, the defending champions. Scoring against them is very difficult."
Santos will be in the quarter-finals if they claim a 1-0 win in the return.
In Porto Alegre, a duel between two Brazilian teams ended in a goalless draw as Internacional and Fluminense failed to find a breakthrough.
Internacional had the best opportunity to win the game, but Fluminense goalkeeper Diego Cavalieri saved a penalty by Argentinian midfielder Jesus Datolo.
The second leg of this match will be played on May 10 in Rio de Janeiro.