LOS ANGELES (AFP) — Japan's Akie Iwai fired six birdies in a six-under par 66 to win the Portland Classic by four strokes and join twin sister Chisato as a first-time LPGA winner in their rookie season on the US tour.

Iwai started the day at Edgewater Country Club with a two-stroke lead and never faltered to finish with a 24-under par total of 264.

Chisato Iwai was among the golfers trying to apply pressure, charging up the leaderboard with an eight-under par 64, but it was American Gurleen Kaur who finished second after an impressive, bogey-free seven-under par 65 for 268.

Former US collegiate standout Kaur, opened with three straight birdies and had four more coming in for her career-best LPGA round.

Akie Iwai became the 10th first-time LPGA winner this season and the fifth Japanese player to triumph.

She said she had felt pressure to join the flood of Japanese winners, but even more she was inspired by her sister's triumph at the Riviera Maya Open in Mexico in May.

"(She) really inspired me," said world number 29 Iwai, who was runner-up this year at Thailand and the LA Championship. "That's why I did my best this year."

Iwai got off to a steady start, with back-to-back birdies at the fifth and sixth and two more at 11 and 14.