The South Korean-born Kiwi teenager carded three-under-par 69 to earn a share of third place, two strokes behind co-leaders Cristie Kerr (66) and Jang Ha-na (69), who set the pace on 11-under 205 at the Tiburon course in Naples.
With a strong final round in the season-ending LPGA event, world number one Ko can win the money list, Player of the Year and the Vare Trophy (for best scoring average).
Most lucratively, she can snag the Race to the CME Globe for the second successive year and collect a $US1 million jackpot that goes to the winner of the season-long points competition.
Ko leads South Korean Park In-bee in three of these four categories, the Vare Trophy being the exception.
But Park is only two strokes behind Ko, and four from the lead with a victory in Naples giving her the jackpot prize, so Ko cannot plan any victory speeches just yet.
"I should be proud that I'm in this position," Ko (18) told reporters.
"Anything can happen. If I play well, it might end up being a good day where I'm holding a couple trophies. At the same time, because everything is on the line, there is more added pressure."
Ko launched a late-season charge with three wins from July onwards (making it six for the year) to overtake Park, who had a big lead in the Race to the Globe when she won the Women's British Open four months ago.
"When I won the British Open, there was so much gap in between me and the other players, I thought somebody had to win at least three or more times to even have a chance," said Park, winner of two majors this season.
"Obviously Lydia was one that was able to do it. It's good that I still have a chance at it."
Not so concerned about the Race to the Globe are Kerr and Jang, who are focused on winning the tournament and it's $500,000 reward.
Two-time major winner Kerr (38) moved within sight of her 18th LPGA victory when she roared back after a three-putt bogey at the first hole to pick up seven birdies.
"I played great," Kerr said.
Halfway leader Jang, meanwhile, overcame some physical ailments to remain in contention.
"A little headache and little dizzy," she said. "Two times my nose bled today."
The LPGA rookie is taking a straightforward approach as she chasing her first victory on the tour after three runner-up finishes this year.
"I don't want to think about another player. Simple thinking is really a very good idea."
