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.

Carlos Alcaraz said Saturday his burgeoning rivalry with Jannik Sinner brought out the best in him, with the Spanish star driven by winning more Grand Slam titles and toppling the Italian as world number one.