Novak Djokovic joined Roger Federer in the last four at 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.
Federer had already won the group but earlier maintained his 100% record with a 7-5 4-6 6-4 win over Kei Nishikori.
Djokovic will face Rafael Nadal in Saturday's semi-final, while Federer takes on Andy Murray or Stan Wawrinka.
The British number one and the Swiss number two will play for the remaining semi-final place at 20:00 GMT on Friday.