Djokovic handed tough Australian Open draw, Sinner faces Jarry test
Italy's Sinner defeated Russia's Daniil Medvedev in last year's final in Melbourne to secure his first major and went on to add the US Open and ATP Finals crowns to his collection.
But the top seed will begin his title defence under a doping cloud after twice testing positive for traces of the steroid clostebol in March.
He was exonerated by the International Tennis Integrity Agency but is awaiting the outcome of an appeal by the World Anti-Doping Agency.
The 23-year-old could meet Greece's Stefanos Tsitsipas or Australian Alex de Minaur in the quarter-finals, and Medvedev in the semis.
Serbia's Djokovic drew American wildcard Nishesh Basavareddy to start but has a huge task in front of him to win an 11th Australian Open and record 25th Grand Slam.
He is seeded to meet world number 10 Grigor Dimitrov in round four and Spain's Alcaraz in the last eight, before a potential clash with Alexander Zverev in the semi-finals.
Alcaraz gets under way against Kazakhstan's Alexander Shevchenko, who scored a confidence-boosting win over world number 11 Tsitsipas at the recent United Cup tournament.
Zverev will meet French wildcard Lucas Pouille.
In the women's draw, world number one Aryna Sabalenka kicks off her title defence against American former US Open winner Sloane Stephens.
The Belarusian top seed is looking to become the first woman since Martina Hingis (1997-99) to win three consecutive titles.
World number three Coco Gauff also faces a tricky start, against 2020 Australian Open winner Sofia Kenin.
But second seed Iga Swiatek was handed an easier assignment against Czech doubles specialist Katerina Siniakova, ranked 46.
However, the Polish star has sixth seed Elena Rybakina and eighth seed Emma Navarro in her half of the draw.
Two-time major runner-up and fourth seed Jasmine Paolini takes on a qualifier, as does Chinese fifth seed Zheng Qinwen, who lost to Sabalenka in last year's final.
In another notable match, four-time Grand Slam winner Naomi Osaka opens against Caroline Garcia in a repeat of last year's first round clash that the French player won.
Should all go to plan, Sabalenka could meet Zheng in the quarter-finals and Gauff in the semis, with Swiatek projected to face Paolini in the last four.
The Australian Open starts Sunday.