Ji's seesaw round included three bogeys, a double and five birdies for a round of even par 71.
BETHLEHEM, Pa. (AP) -- Eun Hee Ji of South Korea made a 20-foot birdie putt on the 72nd hole Sunday, finishing off an even-par 71 to claim the U.S. Women's Open.
The 20-year-old Ji outlasted playing partner and third-round leader Cristie Kerr, who struggled from the outset and failed in her bid for a second Women's Open title in three years.
Ji recovered from two bogeys in her first four holes and a double-bogey at the 10th hole and made three birdies over the final six holes to finish at even-par 284 at Saucon Valley Country Club.
She punctuated her steady back-nine run on the final hole by driving into the center of the fairway, landing her approach about 20 feet from the pin and rolling the birdie try into the center of the cup.
Ji, who won the 2008 Wegman's LPGA, pumped her fists and embraced caddie Zac Austin after the winning putt dropped. Kerr gave the five-year professional a long embrace.
During the trophy presentation, Ji was doused with champagne.
Candie Kung of Taiwan continued a charge up the leaderboard she started in the third round when she vaulted from 37th to a tie for fifth. She completed her round before Ji and Kerr and appeared headed for a playoff after a 2-under 69 left her at 1-over 285.
But Kung's push to the lead fell short and she settled for second when Ji rolled in the winner.
Kerr shot a 4-over 75 and tied In-Kyung Kim of South Korea for third at 2-over 286.
Brittany Lincicome, who made an eagle putt on the 72nd hole earlier this year to win the Kraft Nabisco, placed fifth after a 1-under 70 left her at 3-over 287.
Futures Tour player Jean Reynolds was in the next-to-last pairing, but stumbled in the final round, shooting 6-over 77 for an 8-over 292.
Overnight storms dumped an inch of rain on the Old Course, softening the fairways and making the greens more receptive to shots. But a steady breeze helped dry out the putting surfaces and players continued to struggle on the speedy, undulating greens.
Kerr, the 2007 champion, failed to reproduce the three workmanlike rounds that gave her a two-stroke lead over Ji heading into the final round.
The slow, steady play she used over three rounds to get to 2-under for the only round below par in the championship was missing from the beginning Sunday as she bogeyed the first hole.
After a birdie at the third to get back to 2-under, Kerr had back-to-back bogeys at the fifth and sixth. She dropped into black number for the first time in the championship with a bogey at the 13th.
Her troubles continued down the stretch as she rolled a birdie putt past the hole at the 16th and missed the comebacker, settling for a bogey that dropped her to 2-over. She failed to make lengthy birdie putts at the 17th and 18th.