'My shots were going straight every time,' said the 5-foot-1 Kim, who's made just one bogey the last two days and was the only player in the field to post three rounds in the 60s. 'I'll try to do my best tomorrow.'
Webb, the champion here in 1999, was three-over for the day late on the back nine but birdied the last three holes to salvage an even-par 72.
'I just didn't do enough right,' said the 27-year-old Australian, who has won 26 times on the LPGA Tour but is so far winless in 2002. 'I have to play well or I don't have a chance.'
Kim, tied for the overnight lead with Webb at eight-under par, set up short birdie putts at the first and sixth holes with 11-wood approaches. She pitched to eight feet and rolled in the putt to pick up another stroke at the par-five eighth, then climbed to 12-under with a 20-footer for birdie at the ninth.
Meanwhile, Webb, playing alongside Kim, missed both the fairway and the green in regulation at the par-five fourth, then failed to get up and down to save par. She negated the bogey with a 15-foot birdie putt at the eighth but found herself four behind Kim at the turn.
Webb threatened to fall completely off the radar screen with three bogeys in four holes to start the homeward stretch at Locust Hill. She dropped a shot after hitting into a greenside bunker at the 10th, then posted back-to-back bogeys at 12 and 13, both the result of missed fairways.
Webb managed a late rally thanks to her wedge game. She birdied the 16th after knocking a sand wedge to six feet. At the par-five 17th, Webb came up short of the green but chipped close for another birdie, then made it three in a row with a wedge approach to three feet at the last.
Kim, who suffered her lone bogey after an errant drive at the 13th, notched birdies at the 16th and 17th to keep well ahead of the pack.
The 25-year-old from Seoul is in the midst of her fourth season on the LPGA Tour. She won twice in 1999 and was named Rookie of the Year, then added another title in 2000. Kim came up empty last season despite finishing second three times.
Last week Kim tied for second at the Evian Masters in France, her third top- five finish in 11 starts this year.
Kim owns 11 titles on the Korean LPGA Tour.
Defending champion Laura Davies finished in third place at seven-under. The 38-year-old Englishwoman, who carded a three-under 69 for the second straight day Saturday, needs two more wins or a victory in a major to qualify for the LPGA Hall of Fame.
Juli Inkster, inducted into the Hall of Fame in 1999, was in fourth place at six-under 210 after a 67. Se Ri Pak, the winner of the LPGA Championship two weeks ago, also shot a 67 and finished alone in fifth, eight strokes off the pace.
Full field scores from the Wegmans Rochester LPGA