Mardy Fish will partner with Mike Bryan in the doubles match Saturday as the United States seeks to sweep Roger Federer's Switzerland out of the Davis Cup.
Fish and Bryan will face Federer and Stanislas Wawrinka, the reigning Olympic champions in doubles.
U.S. captain Jim Courier had chosen 19-year-old Ryan Harrison to partner Bryan when the draw was made Thursday. But Davis Cup rules allow lineup changes up to one hour before a match.
Bryan's regular partner, twin brother Bob, is unavailable because of the birth of his daughter last week.
The U.S. leads 2-0 in the five-match series after Friday's dramatic singles matches on an indoor clay court chosen by Federer.
Fish beat Wawrinka in five sets, then John Isner stunned Federer in four.