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

Alcaraz won the French Open and Wimbledon titles last year while Sinner claimed the Australian Open and U.S. Open trophies.

Jannik Sinner will launch his Australian Open title defence under a stubborn doping cloud but the whiff of scandal may do little to halt the Italian juggernaut. Sinner remains the man to beat at Melbourne Park even as doping officials seek a two-year ban for the world number one for failing two drugs tests last March.