Kevin Anderson is in a strong position to qualify for the semi-finals after beating Japan's Kei Nishikori 6-0 6-1 to claim his second ATP Finals win.
The South African, 32, comfortably won the first set to love in just 32 minutes at the O2 Arena in London.
Anderson, ranked six in the world. broke again early in the second set and led 6-0 5-0 before Nishikori finally held serve.
ATP Finals debutant Anderson is top of Group Lleyton Hewitt.
He has not dropped a set after beating Austrian Dominic Thiem 6-3 7-6 (12-10) in his opening match.