After starting the final round in a three-way share of the lead, then surging three shots clear, Lee closed with a shocking eight-over 78 as Saso (68) produced a late birdie blitz to romp to a three-stroke triumph at Lancaster Country Club.

Saso finished with a four-under-par total of 276, with compatriot Hinako Shibuno (72) runner-up and completing the first-ever Japanese quinella at a major – men's or women's.

Americans Andrea Lee (75) and Ally Ewing (66) shared third at even-par for the championship.

After taking a two-shot lead into the back nine, Lee eventually finished in a tie for ninth at three-over.

The 27-year-old's hopes of joining Australian golf royalty with a third career major championship essentially perished in a crushing 15-minute stretch mid round.

Even after racking up a third bogey of the day on the 9th, Lee headed to the back nine two shots in front.

But a sloppy three-putt bogey on the 10th precipitated a shocking meltdown.

Lee dunked her tee shot into the water en route to a double-bogey five on the devilish par-3 12th that brought World No.1 Nelly Korda unstuck on Thursday.

With Saso, playing in the penultimate group behind Lee, posting birdies on 12 and 13, the tournament suddenly turned on a five-shot swing.

It was a day to forget for Minjee Lee at Lancaster CC. PHOTO: Getty Images.

From two behind, where she started on Sunday, Saso was three in front of Lee and the rest of the chasing pack.

Another double-bogey from Lee on No.14 ended all hope of the West Australian joining the great Karrie Webb as a dual U.S Open champion.

A commanding four-shot winner two years at Pine Needles, Lee will now attempt to pick up the pieces from Sunday's collapse ahead of the season's last three major championships and Paris Olympics – all coming in the next two months.

In stark contrast, Lee's Games teammate Hannah Green finished with a flurry to she 16th at five-over following a final-round 66, the equal low round of the week.

But the spoils – and women's golf's biggest winner's cheque for $US2.4 million ($A3.6 million) –belong to Saso.

The Filipino-born star also won in 2021 at the Olympic Club in San Francisco.

At 22 years, 11 months and 13 days, Saso is the youngest player in history to win two U.S Women’s Open crowns – and the first ever to land two majors representing different nations.

"It feels great," an emotional Saso said.

"Winning in 2021 representing the Philippines, I feel like I was able to give back to my mum.

"And this year I was able to represent Japan and I think I was able to give back to my dad.

"So, I'm very happy that I was able to do it. It's just a wonderful feeling that I was able to give back to my parents."

Her latest triumph looked most unlikely after Saso four-putted for double bogey on the sixth to slip four strikes adrift of Lee.

But then everything changed as Lee, striving to join Webb, Jan Stephenson and Peter Thomson as only the fourth Australian to win more than two majors, completely unravelled down the stretch.

– Darren Walton