Isner, instrumental in the U.S. victory over Australia in the first round of the round-robin event in Dusseldorf, Germany, was replaced on the American squad by former top-20 performer Robby Ginepri -- who was outlasted by Spaniard Nicolas Almagro 6-3, 5-7, 7-6 (7-4) in second-round Red Group play.
The Americans did manage a split in Tuesday's singles competition when Sam Querrey posted a 6-3, 6-4 win over Spain's Daniel Gimeno Traver. With the tie, the U.S.-Spain contest will be decided by a doubles match Wednesday.
Germany, meanwhile, posted a 1-0 Blue Group lead against Argentina when Philipp Kohlschreiber defeated Horacio Zeballos 6-3, 6-4, and France ended the day in a 1-1 tie with Serbia after Tuesday's singles rubbers.
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