Mike and Bob Bryan out-dueled Marcel Granollers and Marc Lopez 6-3, 3-6, 7-5, 7-5 to cut Spain's lead in the semifinal round to 2-1.
Spain can advance to the finals with a win Sunday in the reverse singles.
David Ferrer will take the court for Spain against American John Isner in the first match.
After winning the first match Saturday, the Bryans failed to capitalize on any of their nine-break point chances in the second match. Lopez double-faulted in the final game of the fourth set while trying to force a tiebreak to give the Americans the match.