John Isner and Sam Querrey will spearhead a new-look US team in their Davis Cup semi-final in Spain later this month.
The duo will team up with the doubles pairing of twins Bob and Mike Bryan for the Sept. 14-16 tie on clay.
Isner and Querrey will take on the daunting prospect of filling the two singles berths after the retirement of Andy Roddick and the unavailability of Mardy Fish, who pulled out of the U.S. Open this week because of undisclosed health issues.
"This one is the ultimate ask in current Davis Cup tennis," U.S. captain Jim Courier told a news conference on Tuesday. "Going into Spain, playing them on red clay, they haven't lost in a long, long time.
"We certainly feel like we're going to have a chance, but we also feel like we're not the favourites."
Spain won the Davis Cup in three of the last four years, including 2011, but will be without the injured Rafa Nadal for the semi-final.
The winner will play either Argentina or Czech Republic, who meet in the other semi, in the final in mid November.