MOBILE, Alabama, May 19, 2013 (AFP) - Johnson's effort on the par-72 Crossings course at Magnolia Grove gave her a 21-under par total of 267 and her first victory on the LPGA Tour. The 21-year-old American's 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 Ariya Jutanugarn (65) and Sweden's Anna Nordqvist (69).
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.
Leading scores on Sunday after the final round of the Mobile Bay LPGA Classic (USA unless noted, par 72):
267 - Jennifer Johnson 67-70-65-65
268 - Pornanong Phatlum (THA) 69-65-71-63, Jessica Korda 66-65-69-68
269 - Shin Jiyai (KOR) 72-66-68-63, Ariya Jutanugarn (THA) 69-66-69-65, Karrie Webb (AUS) 69-63-69-68, Anna Nordqvist (SWE) 73-66-61-69, Chella Choi (KOR) 67-66-66-70
270 - Stacy Lewis 70-70-63-67
271 - Seo Hee-Kyung (KOR) 68-68-70-65, Lexi Thompson 65-70-69-67
272 - Beatriz Recari (ESP) 68-70-68-66
274 - Mo Martin 70-69-71-64, Azahara Munoz (ESP) 71-64-73-66, Thidapa Suwannapura (THA) 67-67-72-68, Mariajo Uribe (COL) 70-67-68-69, Ji Eun-Hee (KOR) 65-72-67-70, Sydnee Michaels 72-62-69-71
275 - Lisa McCloskey 69-68-71-67
276 - Julieta Granada (PAR) 69-70-67-70, Nicole Castrale 67-69-68-72
277 - Yoo Sun-Young (KOR) 73-69-68-67, Angela Stanford 71-68-71-67, Chie Arimura (JPN) 72-72-65-68, Karine Icher (FRA) 73-68-68-68, Katie Burnett 73-68-67-69, Mina Harigae 67-68-73-69, Meena Lee (KOR) 70-71-65-71, Park Hee-Young (KOR) 67-71-68-71