ATP World Tour Finals
Venue: O2 Arena, London Date: 22-29 November
BBC TV coverage: BBC Two, 22/28/29 November, 1430 GMT
Del Potro's win at the US Open moved him into the top five men in the world
Argentina's Juan Martin del Potro has secured his place at the year-end ATP World Tour Finals in London in November after winning the US Open.
The 20-year-old joins Roger Federer, Rafael Nadal, Andy Murray and Novak Djokovic, who have already qualified.
Meanwhile, Andy Roddick, Jo-Wilfried Tsonga, Fernando Verdasco and Nikolay Davydenko are still in contention to complete the eight-man line-up.
The event will take place at the O2 Arena from 22-29 November.
Del Potro regained a top-five place in the ATP world rankings after his stunning 3-6 7-6 (7-5) 4-6 7-6 (7-4) 6-2 victory over Federer in the US Open final on Monday.
"It's been a dream winning the US Open and beating Roger in the final, and to qualify for London so early is amazing," said Del Potro.
"I played in Shanghai last year and it is such a special tournament. I look forward to playing at the O2 Arena."
The Tour Finals will feature the world's top-eight singles players and eight doubles teams, competing to be crowned 2009 ATP World Tour Champions.
In two contests, each of the players and doubles teams will be drawn to play a minimum of three round-robin matches to determine which four players and teams advance to the knockout semi-finals.
Del Potro could face British number one and home-favourite Murray, who reached the semi-finals on his World Tour Finals debut in Shanghai last year.
Murray slipped from second to third in the world rankings after the US Open, in which the 22-year-old Scot was beaten by Marin Cilic in the fourth round.