The New Zealander holds a one-shot advantage over England's flu-hit Charley Hull with a three-day total of 10-under-par 206 at Sentosa Golf Club.
Thailand's Jeeno Thitikul stormed into contention with the day’s lowest score of 66 to trail Ko by three with 18 holes left to play at the second stop of the LPGA Asian swing.
Making her 11th appearance at the event where her best result came in 2015 in finishing second, Ko is looking forward to finally getting the job done on Sunday.
"I'm excited to be in the final group tomorrow. I've been in the final group a couple times at this event before and I haven't necessarily taken it over the finish line," said the world number three.
"I hope tomorrow is the day to do it."
Hull is bracing for a showdown with Paris Olympic gold medallist Ko after shrugging off the flu to post a bogey-free 68.
"I woke up this morning and threw up. It was just a little bit of a bug but I'm fine," said Hull.
"I like playing with Lydia. She's a really nice person and so down to earth. I want to go out there, play golf, hole some putts and have fun."
Jeeno was in red-hot form as she stormed back into contention after two lacklustre rounds of 71 and 72.
The Thai entered the round tied for 16th but jumped 13 places after carding seven birdies and one bogey on the ninth hole.
"I did not want to think too much about the first two rounds. I was just trying to keep my ball in the fairway today and giving myself birdie chances," said the 22-year-old.
South Korea's Kim A-lim, who topped the leaderboard at the halfway stage, fell into a tie for fourth after carding a 73.
Also lurking on six-under after three rounds was Australia's Minjee Lee.
