Hon overcame a poor first set to overpower Marina Stakusic with the Canadian qualifier forced to withdraw with severe leg cramps while trailing 1-6 6-4 5-3.
The fighting win was the 27-year-old Hon's first success at her home grand slam in six years and triggered an incredible second day for the home hopes.
Hunter, Tomljanovic, men's world No.6 Alex de Minaur and fellow Sydneysiders Jordan Thompson and Rinky Hijikata also joined day-one winner Talia Gibson in advancing to the second round on a banner day for Australian tennis.
Hunter made a triumphant return to centre stage at Melbourne Park, powering into the second round with a straight-sets win over Spaniard Jessica Bouzas Maneiro.
For Hon, it was a welcome change of fortune, with her only previous AO singles win coming in 2020.
The 27-year-old credited a career-best grand slam run to the third round in New York last September for her latest triumph.
"Just having that experience from the US Open definitely helped me in a lot of ways," said Hon.
With the temperature rising in the final set, Hon first had treatment for a sore shoulder before Stakusic was struck down by leg cramps.
She conceded the final point of the seventh game to receive medical treatment, only to retire soon afterwards. The Canadian left ANZ Arena in a wheelchair with Hon lending her assistance.
"Obviously I didn't want to win like that, but I do feel very relieved that I'm through to the second round," said Hon.
"I really hope she does feel better because that was quite a scene out there."
Hunter, 31, missed last year's Open due to a ruptured Achilles tendon and had to come through qualifying this time around.
The former doubles world No.1 fell behind early in both sets but recovered strongly to win 6-4 6-4.
"It means everything to be winning singles matches here in Melbourne," said Hunter.
"I feel like I have had a very up-and-down career, a lot of injuries in my career from when I was 18.
"When I made the third round in 2024, I finally felt like that was my time. I was sitting at career-high ranking, really thought I was going to crack the top 100.
"Then obviously with my Achilles, that was the most heartbreaking thing I've ever gone through in my life, missing Olympics, missing the chance.
"To come back from an Achilles rupture, I don't know anyone who has done it in tennis."
Hunter enjoyed a career-best run to the third round at Melbourne Park in 2024 before bowing out in a tight three-setter to two-time major winner Barbora Krejcikova.
Tomljanovic lost the first set against world No.110 Yuliia Starodubtseva but regrouped for a 4-6 7-6 (7-3) 6-1 victory.
"I'm just so happy to have won that," the 32-year-old said.
As ever, de Minaur was all business in putting American lucky loser Mackenzie McDonald to the sword 6-2 6-2 6-3.
The good news kept coming for the home contingent as Jordan Thompson hit back hard after dropping the first set to Argentina's Juan Manuel Cerundolo to prevail 6-7 (3-7) 7-5 6-1 6-1.
Wildcard Rinky Hijikata joined the party with a rousing 6-3 6-3 6-1 win on Monday night over French southpaw Adrian Mannarino.
While six Australians advanced on day two, three others crashed out.
Aleksandar Vukic lost 7-5 6-2 6-2 to Argentine Thiago Agustin Tirante, teenage wildcard Emerson Jones fell 6-4 6-1 to 17th-seeded Canadian Victoria Mboko and one-time Novak Djokovic grand slam slayer Alexei Popyrin suffered a crushing five-set exit in the last match of the night.
Popyrin failed to take several opportunities in a 2-6 6-3 3-6 7-6 (7-5) 7-6 (10-4) loss to Frenchman Alexandre Muller.
Popyrin led 4-2 in the fourth set, and then 5-2 in the tiebreak, and 5-3 in the fifth, but was unable to finish off Muller.
