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.

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.