World number one Lydia Ko carded a two-under-par round of 70 to take a one-shot lead into the final round of the US Women's Open at CordeValle.

The 19-year-old New Zealander was in a four-way tie for the lead heading down the last where she holed a nine-foot birdie putt to pull ahead on seven under.

"I think the biggest key around today - well, the biggest difference was the wind. I know it was breezy from the mornings. I knew that it would play a lot tougher than yesterday, because the majority of my round yesterday was played in calm weather," Ko said.

"So people, they say it's moving day on Saturday, but it was really tough out there, because the course is drying out, firming up. And it was tough to get near the pins on some holes."

Ko holds a one-shot advantage over 2009 champion Eun Hee Ji and Sung Hyun Park with Brittany Lang and Amy Yang a further shot adrift on five under and Angela Stanford sitting in sixth place on four under.

Ko made a shaky start to the tournament when she was tied for 52nd place after an opening 73 but got into contention with a second-round 66 before moving into the lead for the first time on Saturday.

She made a long downhill putt for birdie on the third but dropped a shot on the ninth before further birdies on the 13th and 18th.

The only other time Ko has held the lead heading into the final round of a major she was beaten in a play-off by Canada's Brooke Henderson at last month's KPMG Women's PGA Championship.

Scotland's Catrion Matthew posted a 71 and moved up into a share of 20th on 216.