The United States chose Boise, Idaho, to host its Davis Cup quarterfinal partly because its high altitude will quicken play. Conditions have already affected the Serbian team. The U.S. squad four big servers and attacking players in John  Isner, Sam Querrey, Bob Bryan and Mike Bryan.

“We are playing in the conditions which are not normal for the tennis,’ Serbian captain Bogdan Obranovic said. “Still, we practice for five days and also doing some fitness. So my players are ready.”

Boise sits at 2,842 feet above sea level, about 866 meters. World No. 1 Novak Djokovic, who grew up in the mountains in Serbia, said Boise will be the highest altitude he's played in his career.

“I played in high altitude before in my life, but not matches,” Djokovic said. “I think in the tour we have Madrid that's maybe 600, 700 meters, but this is the highest that I'm going to play ever in my life  And it makes a difference. You have to put, I think, an extra effort in the adjustment on the court. You have to try to serve well.  It's tough to control.  You can't expect maybe too many long points because the ball travels through the air much faster than in normal conditions.”