Johns Creek, Ga. - A weather siren sounded on the nearby Atlanta Athletic Club golf course as John Isner prepared to serve on match point against Kevin Anderson.

Lightning was in the area. The appropriate answer was one final booming serve from the 6-foot-9 Isner.

Isner had 20 aces as he survived another challenge to his endurance, beating the heat and Anderson 6-3, 6-7 (7-9), 6-3 to advance to the Atlanta Tennis Championships final on Saturday.

With the siren wailing, Isner unleashed a service winner to end the match. He will face Mardy Fish, who upset top-seeded Andy Roddick 7-6 (5), 6-3 Saturday night, in today's final.

Isner gained fame by winning the longest match in history, a three-day, 183-game match at Wimbledon last month. The Atlanta semifinal, played about an hour from his University of Georgia college home, presented a different level of stress for Isner.

The temperature was 96 degrees for the start of the match. On the hard-court surface, the reading reached 147 degrees.

"The conditions were just brutal," Isner said. "It definitely took a lot out of me."

Isner said he relied on his "will to win."

"Even though I am exhausted, I am able to use my energy smartly," he said. "I am able to keep plugging away until I get my break eventually."

Anderson said he went through six or seven shirts and had one drying on a fan if needed. But sweat-soaked shirts were not the only concern.

"I was sweating through my shoes," Anderson said. "I was slipping quite a bit."

Isner beat the 6-foot-8 Anderson of South Africa in a matchup of two of the three tallest players in the ATP World Tour's top 100 rankings.

Isner appeared the most affected by the intense heat in the second set. He couldn't hold serve when leading 7-6 in the tiebreaker. Anderson won two straight points off Isner's serve and then took the set.

The break between the second and third sets combined with cloud cover to give Isner a lift. The shade from the clouds dropped the on-court temperature about 30 degrees.

Isner led 4-3 in the third set before breaking Anderson's serve for a 5-3 lead.

Then came the weather siren on Isner's final serve.

German Open

Jurgen Melzer of Austria will play Andrey Golubev of Kazakhstan for the German Open title in Hamburg.

The third-seeded Melzer beat Andreas Seppi of Italy 6-4, 6-2, while the No. 82-ranked Golubev defeated Florian Mayer of Germany 7-6 (6), 6-4 to reach his first career final.

No. 15-ranked Melzer was a semifinalist at the French Open and won the Wimbledon doubles title this year. He was also a semifinalist in Hamburg in 2004. Seppi had beaten Melzer in their previous two clay-court matchups.

Slovenia Open

Anna Chakvetadze reached her first final in nearly two years, beating local star Polona Hercog 0-6, 6-2, 6-2 in the Slovenia Open at Portoroz.

The Russian will play for the title against Sweden's Johanna Larsson, who advanced to her first WTA final when Ksenia Pervak of Russia retired with a wrist injury while trailing 6-2, 1-0.

Chakvetadze won the last of her seven WTA titles in 2008. A top-five player in 2007, she's fallen to 103 in the rankings.

"I haven't expected such a success," Chakvetadze said, but the final "is a nice reward for my efforts to get back among the best players of the world."

For Larsson, ranked 84th, it has been a blissful month: She reached her first WTA quarterfinals last week in Prague, then her first semis and final here in Portoroz.

Gastein Ladies

Timea Bacsinszky of Switzerland rallied to beat Austria's Yvonne Meusburger 1-6, 6-4, 6-3 to reach the Gastein Ladies final in Bad Gastein, Austria.

In her first final of the season, the second-seeded Bacsinszky will face either Alize Cornet or Julia Goerges. Their semifinal was canceled due to rain and rescheduled for this morning. The final will be played later today.

The 52nd-ranked Swiss player could win her second career title after Luxembourg in 2009.