Green, Kim and Porter all carded first-round five-under-par 67s at the Siam Country Club to be tied sixth in Pattaya.
Green was labouring along at even par through 10 holes before bursting to life and reeling off five birdies on the inward nine.
In contrasting fashion, after opening her round with an eagle three, the 23-year-old Porter drained four birdies in a hot start to more than offset her lone bogey on Thursday.
Fellow Sydneysider Grace Kim, the reigning Evian Championship champ, also mixed six birdies with a bogey to join the pair at five under.
The trio, along with Thai world No.1 Jeeno Thitikul, are two shots behind Japan's Nasa Hataoka, who had eight birdies in a sizzling round of 65, and home hope Chanette Wannasaen.
Thitikul is delighted to be in the mix at her home-town tournament, an event she'd been contesting since she was 14 years old.
"I couldn't believe like time flies so fast," she said after having five birdies in a bogey-free round.
"I mean, yesterday I was just sitting on the couch in the hotel room and imagining I couldn't believe how far that I have been come from 14 to now.
"Tomorrow I'm going to be 23 now. Just grateful for everything that I really put the work in and it just pays off."
Scotland's Gemma Dryburgh and South Koreans Hye-Jin Choi and Somi Lee all notched first-round 66s to share third spot at the $US1.8 million ($A2.6 million) event kick-starting the LPGA Tour's Asian swing.
Dryburgh was five under through four holes after a spectacular eagle-birdie-birdie-birdie start before cooling off.
"It's going to be low scoring so it's nice to get off to a hot start," she said.
New Zealand's former world No.1 Lydia Ko is among the nine players all locked at five under with the Australian trio.
Another Aussie in Steph Kyriacou is tied for 26th at three under and four shots off the pace.
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