Australian Open starts heating up
"A tough little bracket that we have!" Collins said. "I was like, 'wow, I get really great draws now. But if you're trying to win a Grand Slam, you have to beat everyone."
Kerber was one of three past champions making their returns to Melbourne Park for the first time as mothers.
She joined four-time major winner Naomi Osaka as a first-round exit. Caroline Wozniacki, the 2018 winner, has reached the second round.
Last year's runner-up Rybakina advanced 7-6 (6), 6-4 over former No. 1-ranked Karolina Pliskova.
Victoria Azarenka, who won backto-back titles here in 2012 and 2013, won a hard-hitting contest with Camila Giorgi of Italy 6-1, 4-6, 6-3.
Sloane Stephens picked up her first victory at the Australian Open since 2019, beating wild-card entry Olivia Gadecki 6-3, 6-1.
Among the other men advancing, 11th-seeded Casper Ruud beat Albert Ramos-Vinolas 6-1, 6-3, 6-1, No. 13 Grigor Dimitrov overcame Marton Fucsovics 4-6, 6-3, 7-6 (1), 6-2 and Cameron Norrie defeated Juan Pablo Varillas 6-4, 6-4, 6-2.
There were some player complaints about the relaxing of rules that now allow fans to enter and exit arenas after every game, rather than just at the changeovers. But everyone has been warned now. Meanwhile, opinion is divided on the two-level bar beside Court 6.
Regardless, the second round will get underway Wednesday. Threetime major finalist Ons Jabeur is first up on Rod Laver against 16-year-old Mirra Andreeva and fourth-seeded Jannik Sinner opens the program on Margaret Court.
Defending champions Novak Djokovic and Aryna Sabalenka headline the night matches, three days after wrapping up the first-ever first Sunday at Melbourne Park.