Russian Dinara Safina reclaimed first place in the WTA world rankings on Monday, edging back in front of Serena Williams on the eve of the season-ending Tour Championships in Doha.
Safina, who went to the top of the rankings in April but was overtaken by Williams earlier this month after an early exit in Beijing, will end the year as number one if she out-performs Williams this week.
With just 155 points separating the two players in the list published on Monday the destiny of the year-end number one ranking could not be closer, especially as hundreds of points are up for grabs in Doha, even for victories in the round-robin stage.
Williams, who has 11 grand slam titles to Safina's none, is looking to finish the year as the world's number one player for the first time since 2002.
Denmark's Caroline Wozniacki, the surprise US Open finalist, reached a career-high fourth in the rankings.
Wozniacki's preparations for Doha have been overshadowed by a likely WTA investigation into her retirement from last week's tournament in Luxembourg where she quit against Anne Kremer with an injury while leading 7-5, 5-0.
The 19-year-old, who injured herself at 3-0 in the second set, said afterwards that she retired to allow her opponent to play in the next round as she would have been unable to play another match.
