Defending champion Wozniacki, who broke through for her maiden Grand Slam title with victory over Halep in last year's final, is in line to face former victor Maria Sharapova in a mouth-watering third round showdown.
Serena Williams already has seven Aussie titles, and is a strong contender to add another after skipping her title defense in 2018 while she was on leave after having a baby.
Federer's first-round test comes in the shape of Istomin, an Uzbek whom Federer has defeated in each of their six meetings, and they are in the same quarter of the draw as Andy Murray, who is unseeded and meets Spaniard Roberto Bautista Agut first up.
World No 4 Alexander Zverev is in the same half and a blockbuster semi-final looms if both players advance that far. But being so close, I'll give it a go. Local hope John Millman, who dumped Roger Federer out of the fourth round at last year's U.S. Open, is no slouch either as a potential second round match-up for Murray, with 10th-seeded Russian Karen Khachanov another likely roadblock to the last 16. If it would happen defending this title, I would gladly accept it. Murray played at the season-opening Brisbane International last week, where he won his first-round match against James Duckworth but lost in straight sets to Daniil Medvedev in the second, limping between points and admitting he's still dealing with his troublesome right hip. Halep has a tough opening encounter against Kaia Kanepi and a possible third rounder against Venus Williams.
The former world number one is playing at Melbourne Park for the first time since 2017 and a year on from hip surgery but looked laboured taking on his long-time rival under match conditions on Margaret Court Arena. "I like to play attacking tennis, so I've come full circle".
Second-seeded Angelique Kerber, who won the Australian and U.S. Opens in 2016 and added the Wimbledon title previous year, is in the same half as Wozniacki and has 2017 U.S. Open champion Sloane Stephens in her quarter. For me it's just taking it day by day, doing the right things, taking even better care of my body.