Germany's Alexander Zverev got his ATP World Tour Final campaign off to a winning start with a 6-4 3-6 6-4 victory over Croatia's Marin Cilic. Earlier in London, Roger Federer beat Jack Sock in straight sets.
Rising German star Alexander Zverev claimed another impressive victory, beating Wimbledon finalist Marin Cilic in London.
Zverev, the world number three behind Rafael Nadal and Roger Federer, raced into an early lead, taking the first set 6-4, but Cilic roared back to level the match with a dominant second set.
But Zverev, one of four players making their World tour Finals debut this year, kept his nerve to win a tight deciding set and get his campaign off to the best possible start.
Zverev will face Federer next on Tuesday evening, with the winner certain of a place in the last four.
Federer eases past Sock
Federer made a strong start to his bid to cap his golden year with a seventh ATP Tour Finals title as the Swiss star defeated Jack Sock 6-4, 7-6 on Sunday.
Four months after winning Wimbledon for a record eighth time just a few miles across London, Federer is back in the English capital aiming to cap a remarkably successful spell by lifting the silverware at the O2 Arena.
"It's wonderful to be back, especially after missing last year with injury," Federer said.
"I got off to a great start, but the second set was tight. The breaker could have gone either way and in the end he helped me with some mistakes. I'm really happy I got through somehow."
With defending champion Andy Murray, Novak Djokovic and Stan Wawrinka all absent from the Tour Finals due to injury, Federer and Nadal are this year's headline acts.
mds (AFP, Reuters)