The Australian shot a three-under 69 to be one behind a trio of leaders after the opening round at the tricky Oregon Golf Club layout.
Carlota Ciganda, Gemma Dryburgh and Pajaree Anannarukarn lead the event, with World No.2 Jin Young Ko, Perrine Delacour, Mi Jung Hur, Jenny Shin and Paula Reto all joining Oh in the chasing pack.
Oh made a disastrous double bogey on the second hole (her 11th), offset by birdies on the third, sixth, 10th, 12th and 15th holes.
Ciganda, the only member of the winning European Solheim Cup team in the field, had to overcome an early double bogey herself in chilly morning conditions.
“This morning, some shots the ball was flying 10 to 12 metres less, at least for me on the range,” Ciganda said. “I was like, ‘I need to adjust this on the golf course because it is so cold.”‘
Joint leader Anannarukarn is in hot form after winning last month in Northern Ireland for her first LPGA Tour title.
“Just kind of telling myself to finish the 18, honestly,” Anannarukarn said. “It’s a really hilly course and just try to keep myself in the fairway, hit some good shots, and try to get a good speed on the green.”
Brooke Henderson, the 2015 and 2016 winner, was two strokes back at 70 with 57-year-old Laura Davies, Jeongeun Lee6, Ashleigh Buhai and Sung Hyun Park.
Hannah Green, the 2019 Women’s PGA Championship winner, is tied 42nd.
The West Australian shot a one-over 73 to be five behind the pace.
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