Russia's Dinara Safina will replace Serena Williams as world number one in the WTA's next official rankings, the organisation said on Wednesday.

Safina, who has yet to win a Grand Slam event, has risen up the rankings thanks to four WTA singles titles in the past year -- at Montreal, Los Angeles, Berlin and Tokyo.

The full rankings will be officially released on April 20.

The Russian, whose brother Marat was previously a men's number one, was also runner-up in five competitions including the 2009 Australian Open, where she was beaten by Williams, and the 2008 French Open.

"It's a great honour to reach the number one ranking and it is a dream that every girl who has ever wanted to play professional tennis shares," said Dinara in a statement released by the WTA.

"It is even extra special for me since my brother Marat was able to reach number one and I am happy to share this achievement with him."

The rankings system was questioned last week by Williams, who in the past 12 months has won the Australian Open and the U.S Open and was beaten finalist at Wimbledon.

"There's no question that while I am very proud of my results over the past year, I would have liked to reach this achievement in a different manner," said Safina.

"I hope to prove to everyone over the coming months that I merit the honour of being World number one," she said.

An injury-hampered Williams suffered a 6-4, 3-6, 6-1 defeat to Klara Zakopalova of the Czech Republic in the first round of the Andalucia Tennis Championships on Wednesday.