South Korea's Amy Yang and American Sarah Schmelzel, each seeking her first major title, shared the lead after Friday's second round of the Women's PGA Championship while top-ranked Nelly Korda made an epic collapse.

World number 73 Schmelzel, who missed the cut in five of her past seven starts, fired the week's low round, a five-under 67, and Yang shot 68 to each finish on six-under 138 for 36 holes at Sahalee Country Club in Sammamish, Washington.

"It was a little softer this morning. Overall greens were perfect. I was just happy to take advantage of it," Schmelzel said.

"Definitely firmed up out there so if you can hit it well off the tee, I think you can have some shorter irons and you can be a little more aggressive."

Yang, who had the day's only bogey-free round, dropped her approach at the par-5 18th hole inches from the hole and tapped in to claim a share of the lead.

Korda, who has won six LPGA titles this season, was one stroke off the lead when the day began but fired a nine-over 81 -- the highest score of her professional career -- and finished on six-over 150 to miss the cut by a stroke.

Reigning Olympic champion Korda had eight bogeys and a double bogey before making her lone birdie at 18, a tap-in after nearly holing out from a bunker for eagle.

Sharing third on 140, two strokes off the pace, were American Lexi Thompson, Japan's Hinako Shibuno and South Korean Ko Jin-young.

Yang has 21 career top-10 major finishes without a victory, her closest calls being runner-up efforts at the 2012 and 2015 US Opens.

The 34-year-old won her fifth and most recent LPGA title at last year's Tour Championship.

Yang landed her approach at the par-5 sixth hole just outside eight feet then sank the birdie putt and after that made a 43-foot birdie putt at the par-4 seventh.

She pulled within one of the lead by making a birdie putt from just outside 13 feet at the 15th, setting up her closing birdie.

Schmelzel made a 20-foot birdie putt at the par-5 second, made a birdie putt from just inside five feet at par-3 fifth, added another 20-foot birdie putt at seven, then made a four-foot birdie putt at 10 before her lone stumble, a three-putt bogey at the par-3 13th.

The 30-year-old American sank a 10-foot birdie putt at the par-3 17th and dropped her approach inches from the hole for a tap-in birdie at the par-5 18th.

- 'Staying patient' -

Schmelzel managed her best LPGA finish in March with a runner-up effort at the Blue Bay LPGA tournament but has struggled since.

"Just staying patient, working on the same type of golf things," said Schmelzel of her perseverance. "It's a never-ending cycle and I was just reminding myself of that, that it's going to turn around again."

Thompson, who announced last month that this would be her final season, fired a 72. Shibuno shot 70 and Ko fired a 68.

Korda took her second major title at April's Chevron Championship, but she missed the cut at the US Women's Open and last week's LPGA Meijer Classic and has struggled to regain top form.

Even so, Korda's fall was stunning, a third straight missed cut for the first time in her career.

She made bogeys on her first four holes and added another at the par-5 sixth to tumble well off the pace.

After bogeys at the par-3 ninth, par-5 11th and par-4 14th, Korda had slid to the cut line and with a double bogey six at the 15th, Korda soared to seven-over, too much for her to overcome and reach the weekend.

Thailand's Patty Tavatanakit, who also opened on 69, fell back with a 75 on Friday.