Novak Djokovic has joined Roger Federer in the last four of the ATP World Tour Finals with victory over Tomas Berdych in London.
The world number one required just one set to qualify but won his final group match 6-3 7-5 to secure a semi-final tie against Rafael Nadal.
Berdych managed to recover an early break of serve, but Djokovic moved ahead again and clinched the set he required after 42 minutes.
The 30-year-old Czech rallied round and gave a good account of himself in the second set, but saw his serve broken at 5-5 and his Serbian opponent never looked back.
Andy Murray and Stanislas Wawrinka will play for the remaining semi-final place at 8pm on Friday.
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