World number 59 Kang, who has never finished higher than fourth in a LPGA event, had five birdies in her round of 70 on a day of high scoring as wind and rain battered the Royal Liverpool links.
She was joined at the top later by compatriot and 2011 US Open winner Ryu, who also managed five birdies in the poor conditions.
Tseng, winner at Carnoustie last year and Royal Birkdale in 2010, bounced back from a double bogey at 11 with birdies at 12 and 16 for a 72 to finish tied 11th.
Tseng is bidding for her sixth Major championship in the 36th staging of the tournament.
Wales' Lydia Hall and 16-year-old English amateur Charley Hull are among a group of eight players tied for second on one-under.
The pack also including Ai Miyazato, with eight top 10 finishes on the LPGA Tour this year, Korea's Jiyai Shin - winner in 2008 - and Australia's 2002 champion Karrie Webb.
Christie Kerr and Morgan Pressel lead the 34-strong American contingent on level par. The same score as 15-year-old New Zealand amateur sensation Lydia Ko, winner of the Canadian Open last month.
Paula Creamer, after losing the longest play-off in LPGA Tour history on Monday to Shin on the ninth extra hole at the Kingsmill Championship, is a shot further back with compatriot and Solheim Cup team-mate Natalie Gulbis.
The winners of this year's first three Majors - China's Shanshan Feng and South Koreans Sun Young Yoo and Na Yeon Choi - carded 77, 74 and 73 respectively.
And it was a bad day for the big-name Europeans with Catriona Matthew, the last British winner at Royal Lytham in 2009, managing a 76. Scottish compatriot Carly Booth - leader of the European Order of Merit - carded a 77