Russian Mikhail Youzhny upset top seed Novak Djokovic 7-6, 7-6 on Saturday to reach the final of the World Indoor Tournament.
Sixth seed Youzhny, the 2007 champion, next faces Swede Robin Soderling who overcame Nikolay Davydenko of Russia 7-6, 6-4.
Djokovic and Youzhny made sloppy starts, both dropping their first service games.
The Serb was unable to reach the high level of tennis he showed earlier this week and hit a double-fault to lose the first set 7-5 on the tiebreak.
Djokovic then saved two match points before Youzhny won the second tiebreak 8-6.
"It feels great to beat the world number two but I am also really tired," Youzhny told reporters after needing two hours 17 minutes to overcome Djokovic following his near three-hour tussle with Frenchman Gael Monfils on Friday.
"It really was close and his double-fault on set point in the first set felt like a present."
Earlier, second seed Davydenko dropped his first service game to Soderling but regained control to take the opening set into a tiebreak.
Third seed Soderling, who had never won a tiebreak against the Russian in 10 previous meetings, prevailed and a break in the ninth game of the second set was enough to give him victory.
The 25-year-old Swede had started the year with first-round exits in Chennai and at the Australian Open.
"I came here with hardly any confidence after my start of the season and had no idea what to expect this week. But that improved after every round just like my performances," said Soderling.
"Today was my best performance so far and every match is getting better."