Roddick upset by Fish in Atlanta semi-finals

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Mardy Fish extended his winning streak to nine matches by defeating top seeded Andy Roddick 7-6 6-3 on Saturday to advance to the final of the Atlanta Tennis Championships.

Fish will meet second seed John Isner in the final after the towering American overcame stifling heat to beat unseeded South African Kevin Anderson 6-3 6-7 6-3.

Sixth seeded Fish had a poor service game, making just 40% of his first serves, but saved all three break points and broke Roddick in the only chance he received.

"It's not something I try to do, but when I beat (Roger) Federer at Indian Wells I only served at 35 percent," Fish said.

Isner overcame seven break points and sweltering heat in his afternoon match against Anderson to advance to his fourth final of the year.

"The conditions were just brutal," Isner said. "It took a lot out of me (and) without clouds the sun was just beaming down."

Isner had an opportunity to close out the match in the second set and escape the torturous heat when he held match point in the tiebreak but hit a forehand long and Anderson capitalised to send the match into a decider.

Both players battled fatigue in the final set, before Anderson double faulted to allow Isner to convert the only break point opportunity of the set and take a 5-3 lead, which he converted into victory.

"I started well in the third set but then I played an average service game and he took advantage of that," Anderson said.

"I was making him work harder for his service games than he made me work for mine, but he capitalised on the break points and I didn't."