The 23-year-old Sydneysider followed her opening 67 with a four-under 68 in the Meijer LPGA Classic at Blythefield Country Club on Friday.
Her nine-under total leaves her joint second with Englishwoman Lottie Woad (66), only one behind tournament leader Jing Yan (66).
Porter has been a model of consistency this year with multiple top-10 and top-20 finishes. Among her highlights are second-place at the Australian Open, a tie for fifth in the Founders Cup and a tie for ninth at the ShopRite LPGA Classic.
After impressing on Thursday, the world No.77 began with three birdies on the front nine before consolidating with another two, including on the par-five 18th.
Her only bogey on the day came immediately after her birdie on the par-three 11th, before she regrouped with five straight pars.
Fellow countrywoman and major winner Grace Kim also tasted success, shooting a five-under 67 to be four under for the tournament.
The 25-year-old posted two birdies on the front nine before storming home with another four. A bogey on the 17th was her only blemish, which she duly rubbed out on the last with birdie.
Kim, who famously finished her final round eagle-birdie-eagle to clinch her first major at the 2025 Evian Championship, jumped 68 spots in the field and is now tied 22nd.
Karis Davidson followed her 71 with a two-under 70. Her four birdies coupled with two bogeys left her in a tie for 36th.
Major winners Hannah Green (70, 72) and Minjee Lee (74-68) made the cut on the line at two under.
Both took advantage of the par-five 18th to make birdies to squeeze into the field.
Green made three birdies and three bogeys in her even-par 72, while Lee's blemish-free round included four birdies, a week out from the major KPMG Women's PGA Championship at Hazeltine.
Yan had a bogey-free afternoon round to get to 10 under and, like Porter, is winless on the LPGA Tour.
"I feel like I struck it pretty well the last two rounds," Yan said. "And I putted well, so that kind of adds up to birdies."
First-round leader Yan Liu of China is eight under with Minji Kang of South Korea. Liu had a 70, while Kang shot 68.
Kang aced the par-3 15th and then birdied her final three holes to climb within two shots of Yan.
"It's my fourth hole-in-one, actually," Kang said. "The last one was actually two years ago on hole 11 on this course."
with agencies
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