Novak Djokovic made a flying start to his bid for a record fourth successive ATP Tour Finals title with a 6-1, 6-1 rout of Japan's Kei Nishikori, while Roger Federer cruised to a 6-4, 6-2 win against Tomas Berdych on Sunday.
Defending champion Djokovic and six-time winner Federer have dominated the prestigious season-ending event for the last decade, lifting the trophy eight times between them in the last nine years.
djokovic arrived at London's O2 Arena hoping to win the title for a fifth time and in the process become the first player to lift the trophy four years in a row.
The world No.1 showed why he is the firm favourite to do just that, demolishing Nishikori in 65 minutes to record his 23rd successive win and his 79th victory in 84 matches this year.
With two more group ties remaining against Federer and Berdych, Djokovic's stroll by the banks of the River Thames was a significant statement of intent to his rivals.
"No question I played some of the best tennis I've played this year",Djokovic said.
"Undoubtedly it was an incredible performance that I was hoping I could have coming into this tournament, where I'v had a great record in the last couple of years."