Looks like experience might not matter at the U.S. Women's Open, at least not in Thursday's opening round.

Japan's Mamiko Higa shot the lowest round in an open debut with a bogey-free 6-under 65. She was a shot ahead of another first-timer in 20-year-old Esther Henseleit of Germany and 19-year-old American amateur Gina Kim, who played all of two rounds at last year's event in missing the cut.

"This is maybe one of the top highest level (tournaments) I've played in," the 25-year-old Higa said through an interpreter.

None of them appeared rattled by the moment.

Higa had birdies on three straight and five of her first 10 holes to go to 5-under par before most others got started. Henseleit, also bogey free, had two birdies over her final six holes. And Kim had an eagle and four birdies on her final eight holes.

"It feels amazing," said Kim, who helped Duke win the women's NCAA title earlier this month. "This is something I dreamed of as a little girl. So being able to finish out strong like that really shows I'm ready to be here."

Higa tied for the third-lowest round in U.S. Women's Open history. Helen Alfredsson holds the record with a 63 in the opening round in 1994.

Celine Boutier of France shot 67.

Sei Young Kim of South Korea and Azahara Munoz of Spain were tied at 68. A group of seven featuring American sisters Jessica and Nelly Korda and another U.S. amateur in Andrea Lee were tied at 69.

Higa has won five times on the Japan LPGA Tour, including a victory in March, but may be best known in her country for marrying sumo wrestler Ikiori last fall on their shared birthdays of Oct. 11.

She qualified for the Open as a top-five money winner on Japan LPGA and being inside the top 50 in the world ranking. Still, Higa didn't hold much hope that she could succeed on a course she hadn't played before last weekend.

Higa, though, got going quickly with birdies on the third, fourth and fifth holes. She got streaky again on the ninth and 10th, putting a bunker shot within 3 feet for a tap-in birdie on No. 9 and rolling in a 25-footer on the 10th to move to 5 under before much of the field even got going.

Higa struck once more on the par-3 17th with her tee shot landing inside 8 feet for a final birdie.

Higa said she arrived Saturday with few expectations, let alone leading the major event. "I not only golf, but I enjoy the life here," she said through an interpreter. "And I just enjoyed 18 holes today."

The 20-year-old Henseleit was a German youth champion who has had six top-10 finishes in seven Ladies European Tour events this season.

She finished as the first alternate in London qualifying for this event and waited fretfully for several weeks before the call came saying she was in. Like Higa, Henseleit also played without a bogey and moved within a shot of Higa's lead on the par-5 fifth — Henseleit began her round on the 10th hole — when she put her approach inside 3 feet of the cup for a birdie.

"It's a completely new experience for me to play here and the grandstands are huge and very many people around," she said. "But I don't feel like it's too much for me. So I really like that."

Gina Kim had made bogey on her 15th hole to fall back, but struck for the eagle two holes later. She was 141 yards away in a fairway bunker on the eighth hole when her 8-iron landed on the green and tracked into the cup.

"I didn't even realize it went into the hole until people started screaming at the green," she said.

On her front nine, Kim chipped in for birdie from the bunker on the 17th.

Kim had a 25-footer for eagle on her closing hole, the par-5 ninth, and tapped in for birdie.

World No. 1 Jin Young Ko of South Korea, who won the major ANA Inspiration in April, opened with a 72 as did defending champion Ariya Jutanugarn. Augusta National Women's Amateur winner Jennifer Kupcho and NCAA women's individual champion Maria Fassi both played their first rounds as professionals. Kupcho shot a 71, and Fassi had a 72.

Most of those in the afternoon half couldn't have liked the dried fairways and crunch greens baked out in a day of hot, hot conditions. There were just six who teed off later who broke par, compared to 18 among morning starters.

Players faced sticky, humid conditions as temperatures reached the mid-90s. Nelly Korda, four shots behind after an opening 69, thought the bright sun combined with the heat was taxing on players. "I got a little lightheaded toward the end of the round," she said. "But I drank a lot of water."

Conditions are expected to remain similar through Sunday.