Korean Chun, defending champion Thompson tied for LPGA lead

Reigning U.S. Women’s Open champion Chun matched the low round of the day with a bogey-free six-under 65, while defending champion Thompson had 66 at Blythefield Country Club in Grand Rapids, Michigan. At 15-under 198, they enjoy a one-shot advantage over South Korean Kim Sei-young, who equalled the 65 by Chun and Shanshan Feng of China.

"Today my iron shot great,” Chun told reporters. “I like putting very well. I was so good at rolling the ball on the line.” The 21-year-old Chun, a rookie on the LPGA Tour, roared home with birdies at the 11th, 12th, 14th and 15th holes. Thompson started well with three birdies in the first eight holes of her bogey-free round. She has gone 33-under in her last seven rounds at Blythefield. “I just hit a lot of drivers, and if my game's on it comes together,” Thompson said.

Thompson, 21, is seeking her second win of the season and eighth of her LPGA career. Her victory at the Honda LPGA Thailand in late February was the only win by an American on the 2016 LPGA Tour.

Spaniard Carlota Ciganda will start the final round two strokes from the lead, with world number one Lydia Ko of New Zealand four back.

Canadian Brooke Henderson, winner of the major Women's PGA Championship last week, is nine behind.

(Reporting by Tim Wharnsby in Toronto; Editing by Andrew Both)