The two best men's players in the world are reconfiguring the sport before their opponents' eyes. They don't know what to do about it

When Carlos Alcaraz is on court for a training session, perhaps working on his newly revamped service motion, he is doing so to buttress a game already good enough to have won four Grand Slam titles.

Four-times Grand Slam champion Carlos Alcaraz said having a rival like world number one Jannik Sinner was good for his game as it pushes him to be at his best every time he walks on court. Alcaraz won the French Open and Wimbledon titles last year while Sinner claimed the Australian Open and U.

With two-thirds of the Big Three retired, a pair of young stars are building a special rivalry on the ATP Tour as a new year gets underway.