Defending champion beat Juan Martin del Potro 6-3, 3-6, 6-3 and improved to a 2-0 record in Group B. He will meet Stanislas Wawrinka in Sunday semi-finals.
Novak advanced into the Barclays ATP World Tour Finals semifinal with a 6-2, 7-6 (6) win over Czech Tomas Berdych in 1 hour and 37 minutes in his final Group A round robin match at the O2 Arena on Friday.
