Isner, who moved up to ninth in the world after winning the Miami Open last weekend, kicked off the quarterfinals at Belmont University with a victory taking 3 hours, 14 minutes.
The United States has a big advantage at least in world rankings, and John Isner and Sam Querrey have given the Americans a 2-0 lead in the Davis Cup quarterfinals over Belgium.
First, Isner beat Joris De Loore 6-3, 6-7 (4), 7-6 (8), 6-4, and Querrey followed with a straight sets victory, beating Ruben Bemelmans 6-1, 7-6 (5), 7-5 on Friday night to put the U.S. a victory away from reaching the semifinals for the first time since 2012.
"We also know the job isn't done," U.S. captain Jim Courier said. "We also have to close it out, and the sooner the better. We'd certainly like to do that (Saturday)."
Isner, who moved up to ninth in the world after winning the Miami Open last weekend, kicked off the quarterfinals at Belmont University with a victory taking 3 hours, 14 minutes.
"It's big absolutely," Isner said of his win. "The first match is critical. We're in a battle to three points. We have the advantage right now. So I'm very happy I was able to do my part, so to say, to put our team up."
The U.S. came in 4-0 all-time against Belgium in the Davis Cup with Belgium playing without both David Goffin and Steve Darcis because of injuries. That left De Loore, ranked 319th, to take on Isner in a big mismatch on paper.
The American cruised through the first set in 26 minutes. De Loore held serve in the second and with the tiebreaker tied at 4-4, took advantage of consecutive mistakes by Isner.
The American hit a forehand long before putting a backhand into the net on his own serve. Then he missed on a 140-mph serve and hit a forehand into the corner long on set point.
De Loore opened the third set by breaking Isner, taking the game with a forehand winner after pushing the game to deuce.
The Belgian also had a chance to break Isner in the seventh game only to see Isner hold and then break back to even the set at 4-4. De Loore fought off a set point down 15-40 to force a second straight tiebreaker. Isner took the final three points to go up 2-1.
Isner converted his sixth match point with a backhand for the win.
Querrey, ranked 14th in the world, took the first set in 25 minutes. He served up 21 aces and won 83 percent of his first serves. Bemelmans held serve in the second, forcing the set to a tiebreaker before Querrey won the final two points. The third set appeared headed to another tiebreaker until Bemelmans hit a forehand long with Querrey holding the advantage.
"It's always nice going out there up 1-0, and I was fortunate to get a break kind of right out of the chute there and that freed me up," Querrey said.
The winner will play either Croatia or Kazakhstan in the semifinals Sept. 14-16.
The other three quarterfinals all split Friday with Spain's Rafael Nadal, the world's top-ranked player, beating Germany's Philipp Kohlschreiber 6-2, 6-2, 6-3 after Alexander Zverev downed David Ferrer 6-4, 6-2, 6-2. Marin Cilic beat Dimitry Popko 6-2, 6-1, 6-2 for Croatia before Mikhail Kukushkin downed Bora Coric 3-6, 7-6 (5), 6-4, 6-2 tying it up for Kazakhstan.
Italy and France split after Fabio Fognini needed 3 hours, 31 minutes to beat Jeremy Chardy 6-7 (6), 6-2, 6-2, 6-3. France's Lucas Pouille had the lone five-set match of the day, beating Andreas Seppi 6-3, 6-2, 4-6, 3-6, 6-1.
