Phoenix, AZ (SportsNetwork.com) - World No. 1 Lydia Ko fired a 6-under 66 on Thursday and she was among four leaders with the first round of the JTBC Founders Cup suspended due to darkness.

Ko, who won the Women's Australian Open earlier this year, was joined atop the leaderboard at Wildfire Golf Club by Tiffany Joh, Sophia Popov and Kim Kaufman.

Moriya Jutanugarn and In Gee Chun carded 5-under 67s. They share fifth place with Dewi Claire Schreefel, who was in the first group out in the afternoon wave, has played 10 holes of her opening round.

Amy Yang and Ha Na Jang were among seven players that shot 4-under 68. Alena Sharp birdied her first four holes to join that group in eighth place.

World No. 3 Stacy Lewis and defending champion Karrie Webb were 2-under par through six holes and part of a logjam tied for 33rd place.

The start of the round was delayed four hours due to rain. The first round will resume at 10:30 a.m. ET, while round two will start at 1:30 p.m.

Ko dropped in back-to-back birdie chances at 11 and 12 to open her round. She birdied the 15th to move to minus-3 and followed with three pars in a row.

The 17-year-old birdied the first and third to move to minus-5. She also birdied the par-5 fifth. After stumbling to a bogey at the seventh, Ko came right back with a birdie at No. 8. She parred the ninth, her last, to share the lead.

"I left a couple short, right in the gut, and then 3-putted in an area I didn't think I'd 3-putt, but 66 is good. It's great to start this tournament on a positive note," Ko said. "You really don't know what's going to happen. You can have a really good front nine, then things might not go your way on the back. You can't lose your concentration."

Joh posted all six of her birdies in a 9-hole span. After a par at the first, she birdied three of four holes from the par-5 second. Joh drained three straight birdie chances from the eighth to jump to minus-6. She capped her round with eight consecutive pars.

Popov, who was in hospital last week with the flu, did most of her scoring on the front nine. She quickly birdied three of the first four holes. Birdies at the seventh and ninth moved her to 5-under. Popov posted her final birdie on No. 13. She parred her last five holes.

Kaufman, like Ko, started on the back nine. Kaufman tripped to a bogey on her first hole. She erased that mistake with a birdie at the par-4 13th.

She converted back-to-back birdie chances from the 15th and again from the 18th to move to minus-4. Kaufman birdied the fifth and made it two in a row as she also birdied the sixth. She parred her final three holes.

"I had a poor start, and I told myself, I'm not going to have this long day. But it had been a long morning already so wanted to get something going," said Kaufman. "I was patient, rolled in a few birdies, hit it close on a couple holes and played pretty steady after that."

NOTES: Ko's win in Australia was her sixth on the LPGA Tour ... She has finished inside the top-7 in all four of her starts this season, and hasn't been outside the top-9 in her last eight events dating to the end of the 2014 season ... Ai Miyazato had a hole-in-one on the par-3 fourth, while Giulia Molinaro had an ace on No. 17.