Nadal, No. 2 in the world, breezed past Juan Monaco 6-1, 6-1, 6-2, and Ferrer, fifth in the rankings, followed with a tough 6-2, 6-7 (2-7), 3-6, 6-4, 6-3 win over Juan Martin del Potro in the best-of-five Davis Cup final in Spain.
A win Saturday by the Spanish doubles team of Feliciano Lopez and Fernando Verdasco over Argentina's David Nalbandian and Eduardo Schwank would give Spain its third Davis Cup title in four years and fifth since 2000.
Argentina needs to win that doubles match and both of Sunday's singles -- in which Nadal takes on del Potro and Ferrer plays Monaco -- to win its first Davis Cup. The Argentines have finished second three times, including 2008 to Spain.
Nadal rolled through a 2 1/2-hour match with Monaco, winning 75 percent of the points on serve and not facing a break point. He converted seven of his 14 break-point chances.
Ferrer battled del Potro for 4 hours, 46 minutes before claiming victory. He used a 10th-game break in the fourth set to force a fifth set and won four consecutive games in building a 5-1 lead before finishing off the win.