Ryu, who won the U.S. Women's Open last year, sank five birdies against three bogeys in her opening round. Kang, who has never finished higher than 15th in a major tournament, used six birdies in offsetting a double bogey and two bogeys for her share of the lead.
The Royal Liverpool Gold Club was playing tough Thursday with only nine other golfers -- all tied for third at 1-under 71-- breaking par. That group includes Top 10-ranked players Ai Miyazato and Jiyai Shin.
Defending champion and world No. 1 Yani Tseng is among a crush of 17 players at even-par 72.
Kang, 21, had a bogey at the first hole Thursday but posted back-to-back birdies over Nos. 6-7. However, she had a 6 at the par-4 eighth. A birdie at the ninth hole allowed her to make the turn at even.
She also had a birdie at 11 and made a move with consecutive birdies at 15 and 16 before a bogey at 17 slowed her some.
Ryu was also even over Nos. 1-9, with a birdie at 2 and a bogey at 3. Her four second-nine birdies came at 13 and par 5s at 10, 16 and 18. She had bogeys at 14 and 17.