LONDON (Reuters) - Defending champion Stefanos Tsitsipas was placed in the same round-robin group as Rafa Nadal when the draw for the ATP Finals was made in London on Thursday. The Greek will also face Austria’s U.S. Open champion Dominic Thiem, who he beat in last year’s final, and Russian debutant Andrey Rublev in the London group.World number one Novak Djokovic, bidding for a record-equalling sixth title at the event, is in the Tokyo group with Russian Daniil Medvedev, Germany’s Alexander Zverev and Argentine first-time Diego Schwartzman. The ATP’s elite year-ender, celebrating its 50th edition, is being staged at London’s O2 Arena for the final time having moved their in 2009. Next year it will move to Turin.