Ko has participated in 44 tournaments around the world since his last victory.
Danielle Kang, who won last week at neighboring Inverness club, had a 70 and was four strokes behind. Kang got within two shots of the header with a birdie on par 3 14th, but she bogeyed the next and picked up a birdie on the last two holes, both par 5s.
Ko, meanwhile, birdied the 16th and 17th and finished four ahead. Ko was 16 and under 197.
She had a one-shot lead heading into the third round at Highland Meadows and took control early, stretching her lead to three shots on the turn. Unlike the first two laps, when birdies had to keep pace, this lap was all about pars. Ko ran nine consecutive runs until his big end.
LPGA Classic Marathon Open Field Scores
It took the form of a two-player race.
Minjee Lee of Australia had a 68 while Jodi Ewart Shadoff, who started the round one shot behind, struggled with a 73. They were 10 under 203, six shots behind.
Lexi Thompson also lost ground with a 73 and fell 12 shots back from Ko.
Ko was heralded as the future of the LPGA Tour when she won the Canadian Women’s Open as a 15-year-old amateur. She was 17 when she rose to No. 1 in the world and she compiled 14 wins and two majors before she turned 20.
But she has only had one victory in the past four years.
Ko is a double winner of the Marathon Classic. A third win might be just what she needs to get back on track.