Iwai closed her afternoon round at Mississaugua Golf and Country Club with birdies on the par-4 eighth and ninth holes for a seven-under 64 and two-stroke lead.

"Last week I won, but already it's in the past, already past," Iwai said. 

Fifteen-year-old Canadian amateur Aphrodite Deng was tied for second with top-ranked Jeeno Thitikul, Leona Maguire, Gaby Lopez and 2023 winner Megan Khang. 

On Sunday in Oregon, Iwai joined twin sister Chisato as a rookie LPGA Tour winner. The 23-year-old Japanese player had second-place finishes in Thailand in February and Los Angeles in April, then watched her sister win at Mayakoba in May in Mexico.

She's playing in Canada for first time.

"Really beautiful course," said Akie Iwai, a six-time winner on the JLPGA Tour. "Looks like something similar in Japan course."

Chisato Iwai bogeyed Nos.8 and 9 to shoot 75.

Deng was born in Calgary, Alberta, and her family lived in Montreal before moving to New Jersey for her father's work. She mostly lives now in Orlando, Florida, but remains a Canadian citizen and plays for Golf Canada's junior program.

"Just trying to hit each shot and play in the fairway," Deng said.

Thitikul played her first round since taking the top spot in the world from Nelly Korda.

"I think just like another day at work for me," Thitikul said.

Korda opened with a 69.

Slumping Canadian star Brooke Henderson had four birdies and four bogeys in a 71. The 2018 champion won the last of her 13 LPGA Tour titles in January 2023.

"Just grateful we were able to get it back to even," Henderson said.

She played alongside Thitikul and Women's Scottish Open winner Lottie Woad, who shot 75.

Defending champion Lauren Coughlin had a 74. She won last year in Calgary.

Three-time major winner Minjee Lee opened with a two-under 69 and is joint 13th.

Lee is the leading Australian and one ahead of Gabriela Ruffels, who had three birdies and a lone bogey.

Ruffles birdied the par-three third and then made par for the rest of her round to join a large group in a tie for 21st.

Evian Championship winner Grace Kim, Hira Naveed and Cassie Porter all had even-par rounds, while Robyn Choi and Steph Kyriacou are at two over.

Hannah Green had another disappointing start, posting a 74.