Jang won the weather-interrupted Coates Golf Championship in Ocala, Florida, at 11-under 277, edging out Brooke Henderson of Canada by two strokes. Jang, forced to play 30 holes on Saturday after rain had disrupted the schedule, survived another wet day with an even 72 over her final 18 holes for a wire-to-wire victory at the par-72 Golden Ocala Golf and Equestrian Club.
Jang, an LPGA sophomore, had four runner-up finishes last season. She will cash in a US$225,000 winner's check.
The 23-year-old is the second South Korean to win on the LPGA Tour in as many weeks. Kim Hyo-joo captured the season-opening Pure Silk Bahamas LPGA Classic last week.
South Korean golfers also won the first two tournaments of 2015, with Choi Na-yeon and Kim Sei-young doing the honors.
Jang finished the third round tied for the lead with world No.1 Lydia Ko at 11-under. While Ko shot herself out of contention, losing five strokes over 11 holes, Jang couldn't take advantage and managed just two bogeys against no birdie through 15.
Jang finally picked up her first birdie of the day at the par-four 16 to take a one-stroke lead. She then added another birdie at the par-five 18th to close out the two-shot victory.
Henderson reached 11-under through 13 but bogeys at 14th and 17th to finish alone in second.
Kim Sei-young ended tied for third at eight under, joined by Ko and highly-touted South Korean rookie Chun In-gee in her first LPGA appearance as a member. Last year, Chun won the U.S. Women's Open, the oldest ladies' major, as a non-member, and will be playing full-time on the LPGA Tour in 2016.
Julie Yang was the fourth Korean in the top 10 after shooting seven-under 281 to tie two others for sixth place.(Yonhap)