Britain's Andy Murray joined world number one Novak Djokovic and newly-crowned US Open champion Rafa Nadal as definite qualifiers for the ATP World Tour finals on Tuesday but Roger Federer faces a battle to make the eight-man field.
Despite falling at the quarterfinal stage in his defence of the US Open last week, Murray is third in the race to London and guaranteed a spot at the season-ending tournament.
Murray has flourished on home soil this year, becoming the first British male since Fred Perry in 1936 to win Wimbledon and he is now setting his sights on completing a memorable year alongside the River Thames.
"It will be great to compete in London again for the first time since winning Wimbledon," the world number three told the ATP's website.
"It's a key focus for me for the rest of the season and I'll do everything I can to give myself the best chances of winning it. The atmosphere there is always special - to win it would be the perfect way to finish the season."
Federer has been an ever-present at the Tour finals since 2002, winning the event six times, but the 17-time Grand Slam champion is at risk of missing out this time.
The Swiss is seventh on the Race to London rankings, just 130 points ahead of compatriot Stanislas Wawrinka and Frenchman Richard Gasquet also closing in.
Wawrinka has the chance to move above Federer when he competes at the Malaysian Open this month while Gasquet is in action at the Thailand Open where he is defending champion. Federer is not scheduled to play again until the Shanghai Masters in early October.