DOHA - World number one Victoria Azarenka and third-seeded Russian Maria Sharapova moved into the Qatar Open semi-finals on Friday as Serena Williams eyed becoming the oldest woman to take the top ranking. Azarenka moved closer to a successful title defence for the second tournament in a row when she survived a weird umpiring incident and overwhelmed Sara Errani, the French Open finalist, 6-2, 6-2.

The Belarussian's surprisingly emphatic win over the Italian means she has now dropped a mere nine games in three matches, and looks the part of the favourite even though the quarter-final line-up contained the four best players in the world. "She's a great fighter and I'm just happy to get through to the semi-finals again here," said Azarenka, who has established an affinity for the sea air, gentle winter sunshine and slowish hard courts in Qatar.

"I came here to practice before the Australia Open, and I shall be back here to do the same in December." Errani's fighting qualities manifested themselves after she thought she had been unfairly denied a point with an over-ruled line decision in the sixth game, with the umpire oddly asking Azarenka to "help her out".

An argument of several minutes ensued with Errani contending that the incorrect "out" call had interfered with her attempt to return the ball, and the umpire apparently unable to remember if Errani had hit the ball or not. Errani had indeed done so, but may have been unable to return the ball in court anyway.

Australian Open champion Azarenka, however, kept quiet about what she had witnessed, and Errani worked herself up into a feverish sense of injustice. She duly held serve and continued to play spiritedly in many long rallies, without ever being able to find weaknesses in Azarenka's game. The top seed got 72 percent of her first serves in, enabling her to force the issue in the rallies more often, and struck 26 clean winners. More surprisingly, Azarenka also won all of the 14 rallies where she came to the net, not normally one of her strongest areas. She may though have to contend with Sharapova, who has won the Qatar title twice and remains unbeaten in Doha after reaching the semi-finals in the other half with a 6-2, 6-4 win over Sam Stosur, the former US Open champion from Australia.

It was Sharapova's 12th win in three Doha tournaments, and after trampling her way through the first three-quarters of the match, responded well when Stosur finally found a higher gear and almost regained parity just before the end.

Afterwards Sharapova explained why she, Azarenka and Williams have appeared so downbeat about the three-way struggle for the world number one ranking this week.

"Is it great to have the opportunity to come back to that position? I mean, we'd be lying if we weren't," she said, dispelling the impression given by Williams that she no longer cared. "We're excited about having the chance. It's pretty special. But, you know, I have been in that spot before. The ranking is always one of those things where it also depends on the other players' success and the amount of points and the tournaments that they play. That's out of control. I think that's the reason why maybe we're a little bit, you know, not so jumping up and down at this table here." Later Williams, at the age of 31, was aiming to become the oldest player ever to become world number one, during her quarter-final with Petra Kvitova, the former Wimbledon champion.