Hunter, the current world No.122, progressed after Martina Trevisan retired when trailing 6-3 3-0 on Thursday (AEDT).
After successfully getting through two rounds of qualifying for the main draw in Florida, Hunter's clash with the 61st-ranked Italian ended after just 46 minutes.
The 29-year-old Queenslander will next play 20th-seeded American Emma Navarro, who enjoyed a opening-round bye.
Former world No.1 Naomi Osaka posted another victory in her comeback from maternity leave, beating Elisabetta Cocciaretto 6-3 6-4.
Four-time grand slam winner Osaka took just 78 minutes to defeat the world No.51 and remain unbeaten in first-round matches in seven appearances at the tournament.
Massive 🔥— wta (@WTA) @naomiosaka ends a blistering rally with an explosive inside-out backhand winner 😮#MiamiOpen pic.twitter.com/voHMdgiFeUMarch 20, 2024
Osaka started her return 1-3, but came into Miami having won four of her last six matches. Her best result of the year so far is a trip to the last eight in Doha - her first quarter-final since her 2022 Miami Open final run.
Osaka will now have a second-round showdown against another returning mother, Ukraine's No.15 seed Elina Svitolina.
Osaka and Svitolina have evenly split their six previous meetings. Their most recent encounter came in the 2019 Australian Open quarters, which Osaka won in straight sets en route to the title.
Florida native and 2018 Miami champion Sloane Stephens celebrated her 31st birthday with a 6-2 6-3 win against three-time grand slam winner Angelique Kerber.
"A very great day at the office," Stephens said.
"I feel like I had the biggest party ever, and you guys all came out."
Up next for the 2017 US Open champion, who fell in the third round at Indian Wells last week, is Romania's Sorana Cirstea.
2020 Australian Open champion Sofia Kenin was beaten 6-2 4-6 6-3 by compatriot Katie Volynets and Danielle Collins won another all-US clash with Bernada Pera, 3-6 6-1 6-1.
With Reuters.
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