Federer reckons changing of the guard may be imminent

LONDON - After dominating the tennis world for so long, Roger Federer thinks the sport's Big Three could face their toughest challenge yet from a new generation in 2020.

Federer's 2019 season ended with a semifinal loss to Stefanos Tsitsipas on Saturday at the ATP Finals, having seen Novak Djokovic and Rafael Nadal eliminated in the group stage of the tournament this week.

Tsitsipas, a 21-year-old Greek who is playing at the ATP Finals for the first time, is among a handful of up-and-coming talents looking to finally end the unprecedented era of dominance by that trio. Other youngsters at the season-ending tournament include 22-year-old defending champion Alexander Zverev and 23-year-old US Open runner-up Daniil Medvedev.