One of seven former University of Southern California players in the field at the scenic course overlooking the Pacific Ocean, the 24-year-old Nam - from Hawaii - has played more than 100 rounds on the layout during her time there.
Playing in the final group of the day and teeing off on No.10, Nam pulled even with defending champion Ruoning Yin and Madelene Sagstrom with a birdie on the par-3 sixth and took the lead with a birdie on the par-5 seventh. She parred the final two holes to finish at 8-under 134.
Nam rebounded after struggling in the middle of the round. She had a double bogey on the par-4 15th and a bogey on the par-4 first. In late January in Florida, she tied for 57th in her LPGA Tour debut at the LPGA Drive On Championship.
"I've seen every single inch of this golf course, good and bad," Nam said. "It's funny, because in college I never really played well here. This is actually the first time that I think I shot consecutively under par, so I'm a bit surprised myself.
"It's definitely a pretty surreal feeling seeing my name on the top of the leaderboard, especially with all the best players in the world.
"I always knew that I can play out here, but I didn't expect it to be so quick to see my name up on the top of the leaderboard."
Yin closed eagle-birdie-birdie for a 65. The 21-year-old Chinese player began the spree with a 5-iron to six feet for the eagle on No.7 and ran in a 45-footer on the par-4 eighth. Ranked fourth in the world, Yin followed her breakthrough LPGA Tour win last year at Palos Verdes with a major victory at the KMPG Women's PGA.
Sagstrom had three late birdies in the afternoon session. The 31-year-old Swede birdied the par-5 14th and 16th and reached 7 under with a birdie on the par-3 17th.
Rose Zhang (68), Leona Maguire (65) and former UCLA player Alison Lee (70) are at 6 under. The 20-year-old Zhang won the Mizuho Americas Open last year in her first professional start. Lee had a birdie-birdie-eagle run on Nos.14-16 for a share of the lead, then dropped back with a bogey on 17.
Linn Grant (68) and Lauren Hartlage (71) were at 5 under.
Second-ranked Nelly Korda had a late double bogey in a 67 that left her 3 under. She won the LPGA Drive On Championship in January in her last event.
First-round leader Maude-Aimee Leblanc followed her opening 64 with a 79 to make the cut on the number at 1 over. The only player in the field with a bogey-free opening round, the Canadian had nine bogeys on Friday.
Gabriela Ruffels shot 69 after her opening-round 72 to move to 1 under.
Ruffels is the leading Australian and is one ahead of Karis Davidson, who also made 69 after her first-round 73.
After her opening-round 70, Perth rookie Hira Naveed made a disappointing 74.
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