With five weeks to go before the season-ending Masters Cup in Shanghai, six spots in the eight man field remain up for grabs.
Only the world's top two players, Roger Federer and Rafael Nadal, have so far been able to book their flights to China.
While Federer takes a break this week and Nadal aims to win his first title since his French Open triumph in June, many of their rivals are eyeing a place in the Masters Cup as fewer than 90 points separate Ivan Ljubicic (third) from Mario Ancic (10th), in the ATP Race standings.
At this week's Vienna Open, Ljubicic, US Open runner-up Andy Roddick (fourth), Argentine David Nalbandian (eighth) and Australian Open finalist Marcos Baghdatis (ninth) are hoping to boost their chances of joining nine-times Grand Slam champion Federer and Nadal in the November 12-19 tournament.
Roddick trails Ljubicic by two points for third place and both players need to reach the quarter-finals in order to improve their points totals.
Baghdatis stands just one point behind Nalbandian, who is playing in his first ATP tournament since the US Open.
Nalbandian, who beat Federer in a five-setter to win the Masters Cup last year, is 25 points shy of number seven Tommy Robredo, who is off this week. Nalbandian will need to reach the final to pass the Spaniard.
Serbia's Novak Djokovic is also looking to improve his Cup bid this week in Vienna following his win at the Metz Open which pushed him up two places to 18th in the Race. The 19-year-old trails Nalbandian by 122 points in the standings but, having won 18 of his last 22 matches, he could yet sneak into the elite field.
Among those hoping to prevent Nadal from winning his sixth title of year will be James Blake.
The American moved up three spots to sixth after capturing the Bangkok title two weeks ago.
US Open semi-finalist Nikolay Davydenko could overtake Roddick by winning the Kremlin Cup title.
The remaining top 10 players in contention, Robredo and Ancic, return to action next week in Madrid.
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