Brazil left Spain on the brink of elimination from the Davis Cup World Group after Bruno Soares and Marcelo Melo defeated Marc Lopez and David Marrero 6-3, 7-5, 7-5.
The result Saturday gave Brazil a 2-1 lead in their playoff for a place in the competition's elite category next year, reports Xinhua.
Spain, who are without Rafael Nadal and David Ferrer, must now win both of their singles matches Sunday to avoid relegation from the World Group for the first time since 1995.
Soares and Melo secured victory Saturday in two hours and 35 minutes at the Ibirapuera indoor arena.
"The understanding between us is very good," Melo said. "We've been able to draw all of our positive energy and use it to Brazil's favour. The atmosphere here is second to none."
Brazil No.1 Thomaz Bellucci takes on Roberto Bautista Agut and Rogerio Dutra Silva faces Pablo Andujar Sunday.