Isner heroics earn U.S. quarterfinal Davis Cup win in France

(CNN) -- John Isner beat Jo-Wilfried Tsonga in four sets Sunday to secure a superb Davis Cup quarterfinal victory for the United States over France in Monte Carlo Sunday.

Isner, who has broken into the top 10 of the world rankings this year, gave his team an unassailable 3-1 lead with a 6-3 7-6 (7/4) 5-7 6-3 victory on the clay against the world No. 6 to set up a semifinal against defending champions Spain in September.

Bob and Mike Bryan's victory in Saturday's doubles rubber had put the visitors 2-1 ahead, and the much-improved Isner finished the job.

"I had a great week of practice and I was ready to go," said the big-serving Isner, who will be the second seed at this week's U.S. Men's Clay Court Championship.

He has been in top form recently, beating world No. 1 Novak Djokovic in the semis of the Indian Wells Masters last month before losing to Roger Federer in the final.

Isner beat Federer on clay in February as the U.S. defeated Switzerland in the previous round, and he is now looking to be a real dark horse as the buildup to the French Open begins.

France's defeat marked the final match in charge for captain Guy Forget, who has stepped down after 12 years in charge.

"It's been long but it's been fantastic. Thanks to you and because of my friends, it's been the best time of my life," an emotional Forget told the crowd at the Monte Carlo Country Club.

The Americans, who beat Federer's Switzerland in the last 16, will now play Spain in the last four.

In Oropesa del Mar, David Ferrer beat Austria's Jurgen Melzer 7-5 6-3 6-3 to give the Spaniards, who were without Rafael Nadal, a decisive 3-1 lead and home advantage for the semifinals.

In other quarterfinal action, the Czech Republic saw off Serbia, who were missing Djokovic for the tie in Prague.

Seventh-ranked Tomas Berdych beat Janko Tipsarevic 7-6 (8-6) 7-6 (8-6) 7-6 (9-7) to give the Czechs an unassailable 3-1 lead.

It set up a semifinal against last year's losing finalists Argentina, who sealed their passage thanks to Juan Martin del Potro.

The 2009 U.S. Open champion raced to a 6-1 6-2 6-1 victory over Marin Cilic as the home side took a winning 3-1 lead over Croatia in Buenos Aires.

It followed del Potro's straight sets victory over Ivo Karlovic in his opening singles match Friday.

In WTA Tour action Sunday, Serena Williams powered to the title at the Family Circle Cup in Charleston with a straight-sets demolition of Lucie Safarova.

Fifth seed Williams took the clay court event with a 6-0 6-1 win over her Czech opponent in a one-sided final.