Novak Djokovic launched his bid for a record-equalling sixth ATP Finals title by brushing aside John Isner in straight sets on Monday.
Earlier in the same group, Alexander Zverev made it six consecutive wins against Marin Cilic.
The Serbian world number one looked in ominous form at the O2 Arena as he looks to finish his season with a flourish, winning 6-4, 6-3 in a focused and disciplined display.
In stark contrast to second seed Roger Federer, who produced an error-strewn performance in defeat to Kei Nishikori on Sunday, Djokovic hit just six unforced errors and won 86 percent of points on his serve.
He broke the giant Isner in the fifth game of the first set to establish a stranglehold on the match and never looked like allowing the American back into the contest, breaking twice more in the second set to win in 73 minutes.
“The match was great, obviously,” said Djokovic. “I had three breaks of serve of John…