Russian Anna Chakvetadze held off a strong challenge from Poland's Agnieszka Radwanska to reach the second round of the Dubai Championships with a 6-2 2-6 6-4 victory.

The field in Dubai is so strong that world number 19 Radwanska, a quarter-finalist at the Australian Open, needed to qualify.

"She's a tough opponent to play and I didn't have many wins outdoors this year," Chakvetadze said.

"But I was aggressive and I served pretty well and I was fighting to the end, and that's why I won. We both played well and it was a good match to win because you get more confidence."

Seventh seed Marion Bartoli and former world number three Nadia Petrova continued their run of poor form as they both fell at the first hurdle.

Frenchwoman Bartoli, the 2007 Wimbledon runner-up, has won just three of eight matches this year and was beaten 6-1 6-7 6-1 by Francesca Schiavone of Italy.

Petrova's 6-4 6-4 humbling by Slovenia's Katarina Srebotnik signalled her fifth first-round defeat in six tournaments this year. Srebotnik will next face top seed Justine Henin.

"I think the simple answer is that I just feel burned out," said Petrova. "It already started last year, after I got my injuries after the U.S. Open. I could hide it, I could still force myself and make myself focus and try to play my game and try to win. But this year it seems like nothing is working."

Former world number one Amelie Mauresmo has also struggled this year but the Frenchwoman found her groove on Tuesday to pull off a 7-6 6-2 win over Anabel Medina Garrigues of Spain.

Australian Open champion Maria Sharapova was forced to withdraw with a viral illness and blamed her condition on her recent gruelling schedule.

"After having a few really long weeks I feel my body needs a rest," said the fifth seeded Russian.

"I think it's just a lot of flying. I've done a lot of travelling in the last few weeks, going from Israel (for the Fed Cup) back home and really not resting at all, practising right away for Doha and then going there. One way or another it's going to take a toll.

"I'm going to take a week off now and go on a vacation. I'm just going on a spontaneous trip where there's going to be a limited amount of people and a very limited amount of things to do.

"I'll read and just do nothing. That's my goal for the next week so I can come out with a fresh frame of mind."

Her replacement in the draw, Japan's Akiko Morigami, made the most of her late call-up and defeated Hugary's Agnes Szavay 6-1 6-4 to set up a second-round date with Mauresmo.

Eurosport