Bangkok  - Second seed Gilles Simon needed to rally to join Juergen Melzer in the semi-finals of the Thailand Open Friday, producing a 4-6, 6-3, 6-4 comeback over Russian Evgeny Korolev.

Simon completed the first leg of a possible French double at the Impact arena, with holder Jo-Wilfried Tsonga later bidding for the final four against Swiss qualifier Marco Chiudinelli.

Serb fourth seed Viktor Troicki was playing American number eight John Isner to complete the day's programme. Sixth seed Melzer of Austria defeated German Andreas Beck 6-4, 6-2.

Simon, tenth in the world and chasing a spot in the eight-man year-end championships, shrugged off the continual knee pain which he has had to live with the past three months or more.

He spent an hour and three-quarters in constructing his fightback against Korolev, a hard hitter who goes for broke on every opportunity.

"He stayed on his top level for most of the match. He hit as hard as he possibly could on every shot. It was very hard on my knee today - but I didn't feel a thing out there," said Simon.

Simon will need to eventually rest the knee that has troubled him since playing at the French Open, but is determined to get through to the end of the season.

He said that while the 44th-ranked Melzer, who has not dropped either his serve or a set all week will be a challenge, he's ready as he plays in Bangkok for the first time.

"Juergen is a tough opponent, he does well in all phases of the game. But I just finished this win and I haven't thought that far ahead yet.

"He's not going to be easy to play," he said of the winner of their only previous match in 2006.

Melzer will be competing in his second semi-final of the season as he improved to 28-26 in 2009.

"Simon is a talented player with a lot of variety in his game," he said of his next opponent. "But the way I'm playing, he will have to do really well to beat me."

The Austrian fired ten aces and did not face a break point in his victory over Beck. (dpa)