Ko had a five-shot lead to start the third round — seven shots ahead of Maguire — and made a mixture of birdies and bogeys that stalled her round. She fell one shot behind Maguire until chipping to tap-in range on the par-five 17th. She finished with a 70.
They are at 15-under in what shapes as a two-player race for the $2 million.
No one else is closer than five shots. Former US Open champion Jeongeun Lee had a 68 and Gemma Dryburgh of Scotland had a 69 to sit at 10-under.
The forecast for Monday is for rain and 32 km/h gusts.
Despite losing her big lead, Ko was content with her solid round.
“A few putts here and there that could have, should have, would have. Not taking advantage of some of the par-fives - that was probably the few shots that made it a difference during the last couple of days.
“There were some really low scores out there, and I feel like that happens every day, so I knew that even though I had a lead, it could go really quick even if I still played solid.
“It’s not going to be easy, and I just want to play good golf and golf that I don’t regret. And whatever happens, hopefully it swings my way, but if not, I’m just going to try my best and enjoy it.”
Brooke Henderson kept her slim hopes alive for player of the year. The Canadian, who had to withdraw last week with a back injury, had two eagles in her round of 65 and was at nine-under.
Henderson will have to win the Tour Championship and have Ko finish third or worse to win player of the year.
Ko came into the week with a one-point advantage over Minjee Lee for player of the year. Lee, the Australian who won the US Open and leads the LPGA money list, has fallen nine shots behind and is all but certain to be eliminated.
While Ko is still in a strong position to win her Order of Merit title, fellow Kiwi Ryan Fox has fallen out of contention at the DP World Tour Championship.
Fox is at one-under through three rounds of the season-ending event, in a tie for 26th, 14 shots off the lead, and 11 behind Race to Dubai front-runner Rory McIlroy.
McIlroy is well-placed for another Race to Dubai title after his seven-under 65 left him three shots off the lead heading into the final round.
Jon Rahm holds a one-stroke lead after a bogey-free 65 put the Spaniard at 15-under at Jumeirah Golf Estates as he seeks to win the individual event for a third time.
The top-ranked McIlroy will battle US Open champion Matt Fitzpatrick for the season-long trophy.
“If I’m able to go out there and shoot a good score and get the job done, it would be a really nice way to end what’s been a great year,” said the Northern Irishman, who is trying to become the European tour’s leading player for the fourth time in his career.
Fitzpatrick trails Rahm by one shot after a 70 that included two bogeys on the front nine at the Earth Course, where he is a two-time winner.
The Englishman can clinch what would be his first Race to Dubai title if he wins and McIlroy finishes below second. A second-place finish would also be good enough for Fitzpatrick if McIlroy finishes lower than seventh.
“It would mean the world,” said Fitzpatrick, who lamented a slow start. “I’m going to need a lot of things going my way. I’ve given myself a chance going and that’s all you can do from the start of the week.”
Alex Noren (68) is two shots off the lead, and McIlroy is tied for fourth with Tyrrell Hatton (72).
On the PGA Tour, Kiwi Danny Lee is set for his best finish of the season at the RSM Classic. Lee carded a four-under 66 to move to 10-under, in a tie for 17th. Patrick Rodgers and Ben Martin lead by a shot at 14-under.
- With AP
