Sam Querrey and John Isner take aim at world No. 1 Novak Djokovic, whom they will face this coming weekend in Boise when the U.S. plays Serbia in a Davis Cup quarterfinal.

Both Isner and Querrey own wins over the Serbian: Isner upset him in the semifinals of the 2012 Indian Wells tournament, and Querrey beat him in the second round of the 2012 Paris Masters 1000. However, Djokovic is 2-1 against Isner, including a dramatic, five-set victory over the American in Davis Cup three years ago in Serbia on clay. Djokovic is 5-1 against Querrey and beat him in straight sets last month at Indian Wells.

"Sam and I have beaten him before and we will take the court believing we can beat him again," Isner said today.

Isner told the Idaho Statesman that his big serve will be key. As the United States' No. 2 player, he will open up against Djokovic on Friday.

"I don't want to give my opponent too much rhythm," Isner said. "I'd rather me not have rhythm as well as my opponent not have rhythm because most guys I play against want to find that groove in the match and once they do, they're very, very tough to beat. For me, I try to take that away. It's something I know I have to do against Djokovic."