'I think I'm more happy than the first win,' admitted Jang, whose first win came last year at the Women's British Open. 'I don't know why. I was more nervous than the first win.'
Hart, who birdied the 16th and 17th holes to grab her share of the lead, missed a 2-foot par putt on the last hole to get in at 11 under par.
Jang, playing in the final group, had the lead to herself, but fell down the leaderboard at the 15th when her 8-iron tee shot landed in a bunker and she failed to get up and down.
At the par-5 17th, Jang's drive landed in a fairway bunker on the left. She laid up with a 6-iron, then her sand-wedge third hit the pin and stopped 3 feet from the hole. She converted the birdie putt and parred 18 to hold on for the win.
'I was really nervous from the starting hole to the finishing hole,' acknowledged Jang. 'Everything was tough to me. I think after winning, everything makes me relax.'
Hart shot a 3-under 79 and tied for third place with Brittany Lang, who tied for second place last year as an amateur at the U.S. Women's Open. Lang carded a 1-under 71 to join Hart at minus-11.
Mi Hyun Kim only managed an even-par 72 on Sunday and took fifth place at 10-under-par 278.
Jang began the final round in the lead and struggled early. At the first, she hit her drive left and was forced to lay up short of the green. She hit a sand-wedge to 60 feet and two-putted for a bogey.
She recovered on the front nine with three birdie putts from inside 6 feet. However, Lang cruised into the lead with four birdies in a six-hole span before she made the turn.
Lang stumbled at the 13th with a bogey. Things did not get any better as she bogeyed 14 to all but fall out of contention.
Jang did not play much better than Lang. Jang missed another drive left at 10, but reached the fringe with her second. She chipped to 9 feet, but missed the par putt.
Jang recovered with a birdie at 13 when her 9-iron stopped 8 feet from the cup.
Granada, a 19-year-old tour rookie, bogeyed the second, but was flawless from there. Her putter was working as she tallied five birdies from the fourth to 13th holes and only one came from inside 10 feet.
Granada hit a 7-iron at the 18th to 3 feet. She rolled in the birdie putt, but sat and watched as Jang hoisted the trophy.
'I was just trying to catch my breath,' said Granada. 'I wasn't even thinking what she was doing. I was just trying to get myself together if I needed to play a playoff.'
Jang pocketed $270,000 for the win and was just happy to validate her shocking Women's British Open victory from last summer.
'I've been waiting a long time, feels like over a year,' said Jang. 'That's why I think I'm more happy. It's just awesome.'
Lorena Ochoa, the LPGA Tour's leading money winner and the 2005 champion, carded a 3-under 69 and tied for sixth place with Hee Jung Park (65), Sherri Steinhauer (70) and Wendy Ward (71). The group came in at 9-under- par 279.