Top-seeded Russian Nikolay Davydenko defeated Belgian Oliver Rochus 6-4, 6-3 on Thursday to set up a semi-final against fourth-seeded Briton Andy Murray in the Qatar Open.
Murray rallied after dropping the first set to beat Max Mirnyi of Belarus 2-6, 6-2, 6-2.
Second seed Ivan Ljubicic of Croatia will face sixth-seeded Swede Robin Soederling in Friday's other semi-final after defeating Russian Mikhail Youzhny 2-6, 7-6, 7-6. Soederling beat Cypriot Marcos Baghdatis 6-3, 6-2.
Rochus broke Davydenko in the second game of the first set before the Russian, ranked third in the world, broke back in the seventh and ninth games to clinch the first set.
In the second set Rochus got another good start, breaking Davydenko in the sixth game. But Russia's Davis Cup hero broke back in the seventh and ninth again and wrapped up the set with a winner down the line.
"He (Rochus) played a lot of sliced backhands from the baseline and I had to stay focused always." Davydenko told reporters.
Asked about Murray, Davydenko replied: "He plays like a rocket from the baseline. It is important for me to keep fully fit. The cold weather is giving me some pain in my muscles, but I have to stay alert."
Murray, who took time to find his rhythm, got his act together in the second set.
"It was a slow start for me. The conditions were relatively better today, still it was pretty cold out there," Murray said.
The big-serving Ljubicic overcame a spirited challenge from fifth-seeded Youzhny, who took the first set after breaking serve in the third and fifth games.
But Ljubicic came back strongly, serving 18 aces to shut out Youzhny who had his chances in both the second and third sets.
Ljubicic saved a break point in the eighth game of the second set and the second game of the third to wrap up the match.
"I'm still not happy with my serves, but today's match was not all about serves," Ljubicic told reporters. "We played great tennis.
"I was feeling physically better, so I was able to engage him in prolonged rallies."
Soderling, ranked 25 in the world against Baghdatis's 12th, cruised past the Cypriot in straight sets.
"I played an excellent match," he said. "The conditions were much better, there was no wind today."
The Swede told reporters that his immediate goal was to break into the world top 10.
"I know it's tough but I believe I can do it," he said.