Kerr, the 2007 champion, was at 2-under 211, the only subpar score after three rounds at Saucon Valley Country Club as she chases her second title in three years.
Duramed Futures Tour player Jean Reynolds started two strokes off the lead, but stumbled down the stretch. She closed with a bogey at the 15th and back-to-back bogeys at 17 and 18 on the way to a 3-over 74. Shes tied for third at 2-over 215 with Teresa Lu of Taiwan, who had a 1-under 70.
The wind was blowing at the Old Course in the Lehigh Valley, drying out the putting surfaces and adding speed to the testy, undulating greens.
A handful of players took advantage of the U.S. Golf Associations move to shorten the distance of a number of holes to raise the risk-reward factor.
Those who took advantage included the 23-year-old Ji. She offset three bogeys with four birdies for a 1-under 70 and even-par 213 total to earn a spot in the final group with Kerr on Sunday in just her second Open.
Others werent so lucky, namely Paula Creamer.
Creamer teamed with Kerr to make up an All-American final pairing in the third round, but fell out of contention quickly. She had three bogeys on the front nine, a triple-bogey at the 10th and a bogey at 11. Shes at 6-over 219 after an 8-over 79.
Kerr has said all week that she knows what it takes to win the national championship, especially after winning at Pine Needles in 2007. Shes confident her game matches up well against the narrow fairways and tricky greens of Saucon Valley.
The 12-time LPGA winner has played the first three rounds with patience, never getting too aggressive. That plan seems to be working.
Kerr and Creamer bogeyed the second hole, falling to 2 under and 1 under, respectively.
Kerr pushed her lead to two strokes with a birdie at the par-3 fourth and led by three after Creamer made bogey at the sixth. The lead reached four after the 22-year-old made bogey at the eighth.
Kerr saw her lead shrink to a stroke over Reynolds after bogeying the ninth, but she managed to steady herself and play the back nine in even-par, including a birdie and a bogey.
Reynolds, a two-time winner this year on the Futures Tour and its leading money winner, is proving this week she has the talent to make an impact on more than the LPGAs developmental circuit.
She hung within a stroke of Kerr until her 15th hole, when she hit over the green and had a three-putt bogey. The consecutive bogeys to finish the round ended any chance Reynolds had of making the final group in the final round.
The focus Saturday was strictly on golf after a turbulent week during which the championship was overshadowed by a dispute between LPGA commissioner Carolyn Bivens and more than a dozen top tour players who signed a letter calling for her resignation.
The New York Times, citing a source, has reported that Bivens has decided to step down after the Open concludes. Golf Digest had previously reported that Bivens would be replaced, as soon as next week, and cited sources who said the letter from the players was the final blow.
In other finishes of note, Morgan Pressel shot 69 and moved to 5 over, a tie for 11th at 5 over.
Former champion Laura Davies, playing on a special exemption, moved to 7 over after a third-round 73. The 1987 champion is playing in her 24th Womens Open.
Lorena Ochoas early charge from deep in the field came undone on the back nine. The top-ranked Ochoa followed a bogey at No. 12 with a double-bogey at 13th, posting a 2-over 73 and falling to 8-over 221.
Alexis Thompson, a 14-year-old amateur playing in her third Womens Open, had three bogeys on three of the first five holes, four on the front nine and five in the first 11 on the way to a 7-over 78 and a 9-over 222.