Results on the sixth day of the ATP Finals at London's O2 Arena on Friday (x denotes seeding): Singles Group Tokyo 1970 Novak Djokovic (SRB x1) bt Alexander Zverev (GER x5) 6-3, 7-6 (7/4) Daniil Medvedev (RUS x4) bt Diego Schwartzman (ARG x8) 6-3, 6-3 Doubles Group Bob Bryan Mate Pavic/Bruno Soares (CRO/BRA x1) bt John Peers/Michael Venus (AUS/NZL x6) 6-7 (2/7), 6-3, 10-8 Jurgen Melzer/Edouard Roger-Vasselin (AUT/FRA x7) bt Marcel Granollers/Horacio Zeballos (ESP/ARG x4) 6-6 (1/0) - retired afp