South Korea's Chun In-gee blasts an approach shot en route to her course record opening round at the Women's PGA Championship on Thursday

Washington (AFP) - South Korea’s Chun In-gee fired a record-equalling eight-under-par 64 to surge into a commanding five-shot lead at the Women’s PGA Championship on Thursday.

The 27-year-old two-time major champion reeled off nine birdies and only one bogey at Congressional Country Club outside Washington to match the lowest opening round in the history of the Women’s PGA Championship set by Nicole Castrale in 2006.

Chun’s remarkable round was also a course record at Congressional, the historic 98-year-old venue which is hosting a women’s major championship for the first time.

Shrugging off wet conditions that made the course play longer – two inches of rain had been dumped on the layout overnight – Chun’s round erupted just before the turn when she reeled off four straight birdies to move to five under.

A bogey on her 10th hole of the day briefly interrupted her momentum before another trio of birdies on her 11th, 12th and 13th holes took her to seven under.

One more birdie three holes from home left her on eight under.

“I didn’t think about all the history from the course today,” Chun said. “I just keep going to make birdie as much as I can.

“After a lot of rain – course feels longer. I had a couple of good shots with my woods. That’s how I had birdie chance.

“At the same time the greens were softer, so I think it was just good balance.”

Chun’s spectacular round left her five shots clear of compatriot Choi Hye-jin and Thailand’s Pornanong Patlum, who both posted three-under-par 69s.

American Jennifer Chang and South Africa’s Paula Reto were six shots off the lead on two under, tied for fourth.

Nine women – including in-form Jennifer Kupcho, Canada’s Brooke Henderson and defending champion Nelly Korda – seven off the lead after carding one-under-par 71s.

Korda battled through the conditions with three birdies and two bogeys – including a five on the 18th – but was satisfied to duck under par.

However the American admitted she was taken aback by Chun’s blazing opening round.

“Any first round under par is good at a major,” Korda said. “I don’t know what golf course In-gee is playing. She must be playing really well.

“I would think when I teed it up today, I would be very happy with the score that I shot.”

Korda was in no doubt about how rain-soaked course had played.

“Long. It was definitely really, really long,” she said. “Especially for me. I am one of the longer hitters on the tour, and it was long.”

Kupcho, who defeated Korda and Ireland’s Leona Maguire in a playoff last weekend to capture the Meijer LPGA Classic, was also baffled by Chun’s course record score given the conditions.

“It was definitely really windy with a lot of mist and rain. I haven’t played in rain either in a while,” Kupcho said. “A tough challenge out there in the front nine.

“I feel like I played really well. The course is really hard. I don’t really know how In-gee is eight-under right now. That’s definitely an outlier.”