Holder Jo-Wilfried Tsonga moved to within two victories of duplicating his 2008 title at the Thailand Open as he defeated Swiss qualifier Marco Chiudinelli 6-7 (7/9), 6-3, 6-4 on Friday.
The comeback in nearly two and a half hours echoed the struggle of French compatriot Gilles Simon, who also rallied into the final four after engineering a 4-6, 6-3, 6-4 comeback over Russian Evgeny Korolev.
Tsonga notched 20 aces in his heroic effort against the Swiss underdog ranked 116. Tsonga's win was his 43rd of the season against 15 losses.
"I'm playing well, I really hope I can go all the way like last year," said the 2008 Australian Open finalist.
Serb Viktor Troicki, the number four seed, beat American eighth seed John Isner 7-6 (7/3), 6-2 with 13 aces in their first meeting.
Simon, who said that pain from his troubled knee was the last thing on his mind during his one hour and 43 minute victory over Korolev, will face off against sixth seeded Jurgen Melzer of Austria, who beat German Andreas Beck 6-4, 6-2 in their quarter-final.
"Jurgen is a tough opponent, he plays well in all phases of the game," said Simon, making his Bangkok debut. "But I just finished this win and I haven't thought that far ahead yet."
Simon was put on the back foot in the first set by the hard-hitting Korolev, who has now lost all three matches he has played against Simon.
But the Frenchman was slowly able to turn the tide in a battling performance that featured seven aces and three breaks of the Russian's serve.
"I really had to run a lot today," Simon said. "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."
Simon is the only member of the Top 10 yet to win an ATP Tour title this season, standing 34-24.
Melzer won his only previous match against Simon in Bucharest three years ago on clay.
The 28-year-old Austrian, ranked 44 in the world, will be playing his second semi-final of the season after Umag in the summer.
In Bangkok, Melzer dominated Beck with 10 aces while never facing a break point.
"I haven't lost a set or my serve all week," Melzer said. "I'm very happy with this performance. I want to get as far as I can here. I'm confident and I'm looking forward to the semi-finals."