MONTREAL (AFP) - Serbian Jelena Jankovic's latest bid to grab the world number one ranking ended with a quarter-final exit from the 1.34 million-dollar WTA hardcourt tournament here.

Unseeded Slovakian Dominika Cibulkova continued her impressive run this week with a 7-5, 6-2 victory over the world number two and second seed.

Jankovic missed out on a chance to overtake compatriot Ana Ivanovic atop the rankings when she lost in the semi-finals in Los Angeles. Once Ivanovic lost here on Thursday, Jankovic could have accomplished the feat by reaching the final.

She made a good start, winning the first four games and taking a 5-1 lead in the opening set, but she couldn't keep up the momentum.

"I was feeling good, and I was hitting the ball well. But then all of a sudden I just got exhausted, completely lost my concentration," Jankovic said.

"It was hard for me throughout, you know, for that rest of the match to keep up because the points were quite long. The longer the play went, I felt worse and worse."

Jankovic said she hasn't regained her top form after being sidelined by a knee injury suffered at Wimbledon.

"I'm still not in the best physical shape," she said. "I'm suffering in that department. It will take time for me to get that better because at the moment, you know, I'm struggling to play in a high level for two sets.

"If I was playing three sets, I don't know, they would probably take me in an ambulance," she said.

Jankovic has squandered chances to seize the No.1 ranking in four straight tournaments. Prior to Los Angeles, Jankovic could have moved up by reaching the final at the French Open or the semi-finals at Wimbledon.

But she remained philosophical.

"It's OK. Doesn't matter the first ranking, I want to be healthy," she said. "I want to improve. I want to play tennis. I mean, I don't really think about No. 1 or whatever happens. If it's going to happen, it will happen. But at the moment I don't deserve that spot."

Cibulkova booked a semi-final clash with France's Marion Bartoli, who defeated Japan's Ai Sugiyama 6-2, 6-3.

The 19-year-old Slovakian is enjoying a fine tournament. Ranked 31st in the world she has beaten fifth-seeded Rsian Elena Dementieva and Russian Nadia Petrova as she pursues her first WTA tour title.

Bartoli reached the championship at Stanford recently, but the world No. 15 was unable to secure the championship and remains without a title since November 2006 at Quebec City.

On the other side of the draw, seventh-seeded Dinara Safina overcame 12 double-faults to upend fourth-seeded fellow Russian Svetlana Kuznetsova 2-6, 6-3, 6-2.

Safina moved ahead of Kuznetsova in their all-time series 5-4 and moved a step closer to her third title in as many months.

In the semis Safina will face Victoria Azarenka of Belarus, a 6-4, 7-5 winner over unseeded 17-year-old Tamira Paszek of Austria.

Azarenka, 19, has never won a championship, but she has ascended to a career-high ranking of 16th after runner-up performances at Gold Coast and Prague this season.