Their easy 6-1, 6-4, 6-2 victory in Vienna over the Austrian duo of Julian Knowle and Jurgen Melzer gave the reigning Davis Cup champion an insurmountable advantage.
In a dominant performance, they committed only 10 unforced errors, swatted 12 aces and registered five service breaks in a match that lasted just 89 minutes.
The Bryans also clinched America's first title in 12 years last December when they beat a Russian tandem to give the United States an unbeatable 3-0 advantage in the World Group finale in Portland, Ore.
In the dead rubber matches scheduled for Sunday, America's Andy Roddick and James Blake, respectively, will face Austria's Stefan Koubek and Melzer.
The United States, a 32-time Davis Cup champion, improved to 3-0 all-time against Austria, including a 3-2 victory on clay in Vienna in 1990.