Seventeen-year-old Lydia Ko broke free from a late tie with So Yeon Ryu, hitting a wedge to 4 feet for birdie on the 72nd hole on Sunday to win the Marathon Classic.
She became the youngest player to top $1 million in career earnings on the LPGA Tour.
Ryu had poured in a big-breaking, 25-foot birdie putt on the 17th to pull even.
But then Ko stuck her approach at the par-5 closing hole and calmly rolled in the birdie putt for a 6-under 65 that left her at 15-under 269. It was her second LPGA win as a pro to go with the two Canadian Open titles she grabbed as an amateur.
Ryu pushed a 6-footer at the 18th that would have forced a playoff.
Ko was resilient, also shrugging aside a challenge from veteran Cristie Kerr, who pulled into a tie with her on the homeward nine.
Ko is roughly 17 months younger than Lexi Thompson, who previously was the youngest to hit the $1 million mark in LPGA earnings. She has shown incredible consistency in her rookie year on tour, making the cut in all 15 tournaments she's entered. She has six top-10 finishes in addition to her wins, with five of those being top-fives.
Ko, who proudly bears the flag of her native New Zealand on her golf bag, started the final round in fifth place, three shots behind co-leaders Laura Diaz and Lee-Anne Pace.
While they foundered, she crept up the leaderboard with birdies at holes 3 and 4. She tied for the top spot with a 12-foot birdie putt at the par-3 eighth, then took a solo lead for the first time after hitting her approach to 10 feet at the 10th.
Kerr, seeking her 17th career victory, rolled in a left-to-right breaker from 15 feet at the 13th to pull even.
Ko and Kerr traded pars on their next holes before Kerr's approach on the 399-yard, par-4 15th missed the green to the left and settled into heavy rough. Kerr muscled the pitch shot onto the green, but it rolled 6 feet past and she lipped out the par putt.
At the par-4 16th, Ko hit a pitching wedge from 121 yards to 6 feet past the pin, then rolled in the downhill putt for a two-shot lead.
Kerr, who shot a 67, failed to apply pressure when she could not birdie the closing two par-5s.
Ryu, meanwhile, was quietly moving into contention. She parred the first 11 holes, then birdied four of the next six, tying Ko by nailing the big-breaker at the 17th.
Playing in the pairing immediately in front of Ryu, Ko hit three perfect shots on the closing par-5, which is bisected by a large, deep valley with a creek at the bottom. Her 72-yard chip shot nestled 4 feet away and she drilled it into the heart of the hole to regain the lead.
Ryu found trouble off the tee, hitting near a large pine tree off the right side of the fairway. But she was able to cleanly advance the ball, with it barely clearing the creek. Then her third shot ended up pin-high and 6 feet away.
But she pushed the putt off the right edge, the large gallery groaning as the ball rolled past.
The 5-foot-5 Ko was behind the 18th green, trying to watch what happened over a large mass of spectators. She could tell from the sound of the disappointment in the crowd that there would be no playoff.
Ryu finished with a 67 that left her at 270, and Kerr was next at 272. Kelly Tan (67), Katherine Kirk (68) and Pace (71) were at 273.
Pernilla Lindberg matched Ko for the day's low round with a 65 and she led the group at 274, which also included last week's Women's British Open champion, Mo Martin, who had a 69.
Toronto's Rebecca Lee-Bentham carded a final round 68 to finish in a tie for 12th - her best result of the season and her second best career result since a tie for 11th at the Evian Championship last September.
Maude-Aimee Leblanc of Sherbrooke, Que. slumped to a 72 and into a tie for 54th. It was only her second weekend result in six starts this year.
Diaz, who led almost from the start after birdieing her first five holes on Thursday, lapsed to a 75 and finished at 277.
The start of the final round was delayed an hour by heavy fog.