Nelly Korda credits sister Jessica after firing low second round at U.S. Women's Open

Nelly Korda roared back into contention at the U.S. Women's Open after producing the lowest round of the day on Friday at Riviera Country Club.

After a frustrating opening-round performance left her playing catch-up, Korda responded in style with a superb four-under-par 67, climbing into a tie for ninth place and moving to within two shots of the halfway lead.

The world number one carded five birdies during a polished second-round display and revealed that a range session with her sister, Jessica Korda, helped spark the turnaround.

Korda said she made a subtle grip adjustment after Thursday's round as she continued to battle a swing issue that has frustrated her for several weeks.

"Actually, a big shout out to my sister because she helped me," said Korda. 

"I just tried to strengthen my grip a little bit. I've been grinding on it for five weeks and I can't get it. I don't know what I'm doing in my swing, so I just tried to strengthen my grip. It felt super funky today, but I just trusted it and went with it."

The change paid immediate dividends as the 27-year-old American  looked far more comfortable off the tee and credited the adjustment for helping eliminate some of the misses that plagued her opening round.

"I still hit a few out right today, but it was much, much better," Korda added. "Got a little bit of something going."

Korda's turnaround leaves her firmly in the hunt heading into the weekend, with the tournament remaining tightly packed at the top of the leaderboard.

She is seeking a first ever U.S. Women's Open title this Sunday, and a fourth career major. 

China's Ruoning Yin and Alison Lee share the lead at four-under par after 36 holes.

Yin produced a bogey-free round on Friday to secure her place at the summit and believes patience will be crucial over the final two rounds.

"It's a major, it's tough," said Yin. "I think everybody is aware of that. All I need to do is just stay patient because I know my game is right there."

Lee, meanwhile, continues her bid for a breakthrough first LPGA Tour victory despite entering the week ranked 145th in the world. 

The American mixed four birdies with a lone bogey during her second round to remain tied for the lead.

"Realistically, I thought a few years ago when I became a mom, I wouldn't want to come back and play," Lee said. "I thought it would be too difficult.

"I still have yet to win on the LPGA Tour. That's been my biggest goal since turning pro."

First-round leader Jennifer Kupcho slipped back into a six-way tie for third place, while defending champion Maja Stark sits tied for 24th after a second-round 71 that included an eagle at the par-five 17th.

But the story of Friday belonged to Korda, whose sparkling 67 has reignited her hopes of adding a U.S. Women's Open title to her growing list of achievements.