The United States completed its 5-0 rout of Switzerland in the first round of the Davis Cup on Sunday, with 19-year-old Ryan Harrison and John Isner winning the closing singles matches.

Harrison made his Davis Cup debut, defeating Michael Lammer 7-6 (0), 7-6 (4) to extend the Americans' lead to 4-0. Isner, who stunned Roger Federer in four sets Friday, then beat Marco Chuidinelli 6-3, 6-4 to give the U.S. its first sweep since a 2004 first-round series against Austria.

"It was really exciting to be out there," Harrison said. "To be part of this week was a huge experience."

The U.S. will play at France in the April 6-8 quarterfinals. In other pairings, it's: Argentina vs. Croatia, Austria vs. Spain and Czech Republic vs. Serbia.

Harrison was selected by captain Jim Courier after the U.S. sealed its victory Saturday, when Mardy Fish and Mike Bryan beat Olympic doubles champions Federer and Stanislas Wawrinka. Federer and Fish had been scheduled to meet in Sunday's first match.

Courier praised Harrison's maturity and all-around game.

"You see the weapons. He has got a lot of upside and I look forward to sitting on the bench and watching it firsthand," Courier said. "This was a great experience for Ryan and for me."

Harrison, ranked 95th, dominated the first-set tiebreaker against the 251st-ranked Lammer with volley winners and strong serves, clinching it with a powerful passing shot.

"I got the first point off and that was pretty big. After that, it just kind of flowed," Harrison said.

Courier, a Davis Cup and four-time Grand Slam winner, suggested the 17th-ranked Isner is on the verge of a career breakthrough.

"I learned that John can beat anyone at any time, because no one has a chance if he plays the way he plays, and serves the way he serves, unless they play incredible defensive tennis," Courier said.

Isner cruised against Chiudinelli, the 190th-ranked childhood friend of Federer, and served his ninth ace on match point.

"I definitely played top-notch tennis this weekend in tricky conditions — in Europe, in February, on clay," Isner said. "No matter the surface, no matter the opponent, a lot of times the ball, the point, the match is going to be in my control."