Sue Barker presents live coverage of the group stages of the ATP World Tour Finals, which sees the top eight players in the world battling for supremacy in London. In 2012's tournament, Novak Djokovic underlined his position as world number one by beating Roger Federer in straight sets in the final. With Wimbledon winner Andy Murray absent through injury, the world's top-ranked duo Rafael Nadal and Djokovic are tipped to do battle for this year's crown. Show less