Kim, in the hunt for her first LPGA major, was part of a three-way tie for the lead late in the day with Lewis and Morgan Pressel but moved ahead as her American rivals faded over the closing holes.
The South Korean carded a 69 for a 10-under-par total at Mission Hills in Rancho Mirage, while Lewis (68) was alone in second on seven-under after two late bogeys.
Pressel (71) also had two late bogeys to fall four shots off the pace, equal third with compatriot Brittany Lincicome and Thailand’s Ariya Jutanugarn.
Kim, a five-time winner on the Korean Tour, admitted she would be very nervous in the final round, when strong winds are forecast to buffet the course.
“Those two birdies give me a wider lead going into tomorrow, but that doesn’t necessarily mean that it gives me less pressure or gives me more confidence,” the 22-year-old told reporters.
“I don’t think I’ve ever won a tournament leading the final round.
“Back in Korea when I was playing on the Korean Tour, I was known for coming from behind and winning tournaments. But to be in the lead going into the final round on the LPGA is fairly new for me.”
Kim has already won once this year in her rookie season as an LPGA member, at the Bahamas Classic in February.
A victory on Sunday would make her the seventh South Korean-born winner in eight LPGA events this year.
She was more steady than spectacular for most of the day, using her reliable cross-handed putting stroke to brush in a 20-foot birdie from the fringe at the 16th hole and a 10-foot birdie at the 17th to gain the three-shot cushion.
Lewis, on the other hand, bogeyed two of the final four holes, though it could have been worse.
Her drive at the 15th was headed out of bounds until it hit a palm tree and ricocheted back into a fairway bunker. She bogeyed the hole but avoided complete disaster.
The 2011 champion sounded upbeat about her chances of catching Kim.
“Three shots on this golf course is not a lot,” Lewis said.
“I’ve trailed by more and I’ve won. On a hard golf course when you have a big lead, it’s hard, because you start protecting a little bit, then you start making bad swings.” – Reuters
Original source: Kim grabs 3-shot Inspiration lead