Jang was one of just six players who scored under par during the round, which was hampered by rain, chilly temperatures in the 50s and a pesky wind.
'It was tough, but you know it's the same for everyone out there,' said Liselotte Neumann, who shot a 1-under-par 71. 'I'm pretty happy with the 1 under today...could have been a few better, but I'm in the red, so that's good.'
Sophie Gustafson stands alone in second place after a 3-under-par 69, and Nicole Perrot is third at minus-2. Neumann, Kim Williams and Emilee Klein are one stroke further back.
Fifteen-year-old amateur Carlota Ciganda is among a group of three golfers in the clubhouse with an even-par 72, along with Ai Miyazato and Linda Wessberg. Moira Dunn was even par through 10 holes when play was suspended.
Everyone else was above par, with scores reaching as high as Laura Cabanillas' 18-over-par 90.
'Obviously the course was playing very different from the practice round,' said Annika Sorenstam, who began the quest for her third major this year by shooting a 1-over-par 73. 'The par-fives you can reach in two all of a sudden you're having trouble reaching in three.'
Jang fared a little better, though.
The 25-year-old Korean eagled the par-5 sixth to get to 1 under, knocking her 3-wood within 25 feet before sinking the putt. She moved to 4 under with birdies at Nos. 11 and 12 before dropping a stroke at the par-4 13th.
Jang, who has never won on tour, got that stroke back with a birdie at the next before closing out her round with another birdie at the last.
'I think about winning every week, but that is not really working so I am not going to think about winning this week,' said Jang. 'I am just going to try to maintain my position and golf my ball.'
Michelle Wie -- the better-known 15-year-old amateur -- finished in a group tied at 3-under-par 75.
'Well, I've played in rain before. I've played in the wind before. I played when it was cold before. But all put together was really hectic,' said Wie. 'It's so hard to get a rhythm out there.
'It's the first time I played in the British Open and I felt like I got the whole package.'