Britain's Jamie Murray won on his debut at the ATP World Tour Finals as he and doubles partner John Peers beat Simone Bolelli and Fabio Fognini.
Scot Murray and Australian Peers beat the Italian duo 7-6 (7-5) 3-6 11-9 in a dramatic opening match at London's O2.
That gives them an early lead in the round-robin stage, with Bob and Mike Bryan to face Rohan Bopanna and Florian Mergea later on Sunday.
Top seed Novak Djokovic plays Japan's Kei Nishikori in the opening singles.
Six-time champion Roger Federer will take on Czech Tomas Berdych in the evening session at 20:00.