The No.9 seed needed just 55 minutes to storm to a 6-0 6-1 victory to set up a meeting with Caroline Garcia in round two.
This was only Raducanu's eighth appearance in a WTA main draw and the 19-year old had not played since November having contracted COVID-19 and then withdrawn from the Melbourne Summer Set last week.
Rybakina lost only 11 points on serve in the match, sending down four aces. Raducanu, by contrast, struggled badly: the Briton gave up six double faults and won just two points behind her second serve.
"My serve is a weapon, so I'm always working on it and trying to find some variety," Rybakina said. "For sure, it's my game to play aggressive and my serve is helping a lot."
Elsewhere in Sydney, Olympic gold medallist Belinda Bencic beat Beatriz Haddad Maia 6-3 6-2 in her first match of the year and will now face France's Oceane Dodin.
Home favourite Ajla Tomljanovic defeated Anna Karolina Schmiedlova in straight sets, while world No.20 Elise Mertens also progressed.
At the Adelaide International 2, Coco Gauff looked in strong form as she dispatched Katerina Siniakova 6-1 6-2, while fellow seed Tamara Zidansek beat Heather Watson in a three-set battle.
There was a shock for No.1 seed Aryna Sabalenka, though, as she fell 5-7 6-1 7-5 to Sweden's Rebecca Peterson, who celebrated her first win over a top-five player, while American Lauren Davis beat No.7 seed Jil Teichmann in three sets.
No.9 seed Sorana Cirstea lost in straight sets to Anhelina Kalinina, but No.8 seed Liudmila Samsonova beat Mayar Sherif.