(Reuters) – China’s Shanshan Feng shrugged off the effects of jet lag to fire a six-under-par 66 and seize the early first-round lead in hot, steamy conditions at the U.S. Women’s Open at Trump National Golf Club on Thursday.

The Olympic bronze medalist took advantage of calm morning conditions with a sizzling opening nine of five-under 31. She leads a pack that includes world number one Ryu So-yeon, former number one Lydia Ko and perennial Women’s Open contender Amy Yang.

Feng, who played a tournament last week in China and arrived in Bedminster exhausted on Monday after an overnight flight, birdied three in a row starting on the 11th, her second hole, and then made another birdie trio from the 17th through the 1st in a bogey-free round.

“I had three birdies in the first four holes and then after that I just felt so comfortable about everything,” said 27-year-old Feng, who had never broken 70 in 10 previous Women’s Open appearances.

Other top contenders also took advantage of the rain- softened layout 50 miles west of New York City.

South Korean Yang, who has finished top four in all but one of the last five championships, stood one stroke back after carding a five-under 67.

Ryu, winner of this year’s ANA Inspiration major, birdied three of her last five for a 68. New Zealander Ko slipped from six under with two late bogeys for her 68.

Ko bogeyed the last after hitting a wedge from the fringe well past the hole, rather than putting through the frog’s hair.

“Obviously a little disappointing to finish up with a bogey on the last, but when I see how many good par saves I made throughout the day, I’m OK with that,” the 20-year-old said.

Ko, silver medalist at the Rio Olympics, played in a group with Feng and gold medalist Park In-bee (77) in an Olympic podium threesome.

“Shanshan is one of the most consistent players on tour,” Ko said. “When she was making birdies, I tried to feed off that. When somebody in your group is playing good, I think it just kind of sets a tone for the day.”

Feng took it relatively easy after arriving in Bedminster, limiting herself to nine holes of practice on Tuesday and Wednesday while putting in extra time to work on her putting.

“It was my sponsor’s tournament in China last week and I felt like it was my responsibility to actually go support my sponsor,” Feng said about playing in the Kumho Tire Ladies Open.

“Also, that was my first time to play in China this year, so I really wanted to see my family and all my friends back home.”

Feng said it proved to be a good warm-up for her – the course was narrow and forced her to hit the ball straight.

“I think that was one of my keys, why I actually played well today because I left myself birdie chances for most of the holes,” she said.