Novak Djokovic v Rafael Nadal and Roger Federer v Stan Wawrinka at ATP World Tour Finals

The ATP World Tour Finals semi-finals kick into gear on Saturday with four of the world's best players in action.

Andy Murray might be gone but his greatest rivals will go toe-to-toe for a place in the O2 Arena final up for grabs.

You can watch the ATP World Tour Finals on Saturday - Novak Djokovic v Rafa Nadal is live from midday on Sky Sports 3 HD then Roger Federer plays Stan Wawrinka, live on Sky Sports 3 HD from 6pm.

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Nadal has enjoyed a successful week so far, winning all three matches including one against Murray. His head-to-head with Djokovic is fascinatingly poised - he leads 23-22 ahead of their latest meeting.

Then it's time for Switzerland's top two players, Federer and Wawrinka, to vie for a place in the final. They haven't always enjoyed the most cordial of relationships making their semi-final clash perfect Saturday night viewing.

Live Tennis: ATP World Tour Finals

You can watch the ATP World Tour Finals on Saturday - Novak Djokovic v Rafa Nadal is live from midday on Sky Sports 3 HD then Roger Federer plays Stan Wawrinka, live on Sky Sports 3 HD from 6pm.