Doha: Nikolay Davydenko of Russia defeated Sweden's Jonas Bjorkman 6-4, 6-3 on Wednesday, leading the top six seeds into the quarterfinals of the US$1 million Qatar Open.Second-seeded Ivan Ljubicic, No 3 Marco Baghdatis and No 4 Andy Murray also advanced with straight-set victories, while fellow seeds Robin Soderling and Mikhail Youzhny likewise reached the last eight.Davydenko, who next plays Olivier Rochus of Belgium, used his baseline play to subdue Bjorkman, earning a break in the seventh game and holding the rest of the way to win the first set.The Russian overwhelmed the Sweden national with his forehand in the second set, earning breaks in the first and third games and forcing Bjorkman into errors, such as the two double faults in the ninth game which Davydenko won at love.Ljubicic won 84 percent of the points on his first serve and defeated Younes El Ayanoui of Morocco 6-3, 6-4 in one hour, 15 minutes."I am getting better day-by-day," he said. "It is not easy to play well after a long break but I am doing that. I am also happy that I am back to peak fitness."Ljubicic used his backhand to maximum effect but said he was unhappy with his serve. "It is an area I need to work on," he said.Ljubicic next plays fifth seed Youzhny, who defeated France's Gael Monfils 6-4, 6-2.Baghdatis beat Ruben Ramirez Hidalgo of Spain 6-2, 6-0 while Murray ousted Belgium's Christophe Rochus 6-1, 6-3.Cyprus' Baghdatis, the Australian Open finalist last year, was pleased with his display. "I am moving and serving better," he said. "It is good to play well in the first week of the season. It shows that I am ready for the Australian Open."However, Murray was not satisfied with his one hour 23-minute effort against Rochus. "I made too many unforced errors," the Briton said. "I also need to work on my concentration. I lost focus when I should have finished off the match after leading 4-1 in the second set."Murray next will take on Max Mirnyi of Belarus, who beat Swiss Marco Chiudinelli 6-3, 6-3. Baghdatis will play No 6 Soderling, who rallied past Spain's Guillermo Garcia-Lopez 4-6, 6-0, 6-3.In the day's other match, Olivier Rochus beat Italian Federico Luzzi, 6-1, 6-0.