American Jennifer Johnson fired a seven-under par 65 on Sunday to seize her first LPGA title, posting a one-shot victory over PornanongPhatlum and Jessica Korda in the Mobile Bay Classic.

Johnson had eight birdies and just one bogey on the par-72 Crossings course at Magnolia Grove for a 21-under par total of 267. "I'm a little shocked, I didn't even realize I shot 65," said the 21-year-old, whose previous best finish was a tie for eighth at Prattville, Alabama, in 2011. Her total of 267 bettered the tournament's scoring record by four strokes.

Thailand's Pornanong climbed up the leaderboard to seize her share of second place with a nine-under par 63. After opening with a bogey at the par-four first she had 10 birdies, including three in a row to end her round. She was joined on 268 by Korda, who started the day one off the lead and had seven birdies in a four-under 68. Overnight leader Chella Choi of South Korea carded a 70 to finish in a group of five players sharing fourth place on 269. She was joined by compatriot Shin Jiyai (63), Australian Hall of Famer Karrie Webb (68), Thai teenager AriyaJutanugarn (65) and Sweden's Anna Nordqvist (69).

At the turn, Johnson was one stroke behind Korda. She said she began thinking seriously that she had a chance to win when she sank a 15-foot birdie putt at the 17th to get to 21-under. Even before she made that putt, she had seen that Pornanong, playing several groups ahead of her, had reached 20-under. "Oh, yeah, I was definitely aware," Johnson said. "Before I hit my birdie putt on 17, I saw that Pornanong was tied with me at 20 and I didn't want a playoff so I was like, I'm going to make this thing." Johnson had to wait for the final two groups to finish to be sure she'd done enough, and said she'd try to take time to enjoy the victory. "I'll try to, but I'm always looking ahead," she said. "I've got to try and relax more. It means a lot. Since I played my first tournament, I was nine, and when I was about 12 or 13 I wanted to play on the LPGA. So like nine years, this is kind of what I've worked for." Stacy Lewis, who set the previous tournament scoring record of 271 in winning last year, carded a final-round 67 to finish alone in ninth on 270.