With just one more event remaining in the 2014 LPGA season, Ko has a shot at claiming the US$1 million payout for the season-long points leader. She needs to finish well in Mexico and then win next weekend's CME Group Tour Championship in Florida.
Kim has one of the longest winless droughts on the tour - her last victory coming almost a decade ago at the Tournament of Champions - and she came under pressure today from Creamer.
Norway's Suzann Pettersen also had a strong day, shooting a six-under 66 and jumping into a tie for third with Ko, Thailand's Pornanong Phatlum (68) and Spain's Azahara Munoz (71). World No 1 Inbee Park was 10th, six shots behind Kim, and No 2 Stacy Lewis was in a tie for 27th at two-over.
Meanwhile, Kiwi professionals Danny Lee and Tim Wilkinson were in the hunt at the halfway stage of the OHL Classic in Mexico on the PGA Tour.
Lee (66, 69) and Wilkinson (68, 67) were in a share of 16th, five strokes behind American Michael Putnam on 12-under par.
Lee, who is 76th in the early stages of the Fed Ex Cup, made four birdies and two bogeys in his second round to drop nine places down the leaderboard.
Wilkison, who is currently tied 99th on the season money-list, had five birdies and a bogey in his four-under par 67.
Waikato professional Steven Alker bounced back in round two with a five-under par 66 but still missed the cut by one stroke.
Elsewhere, Ryan Fox's dream of joining the Web.Com Tour in 2015 is over.
The 27-year-old, who had carded rounds of 72, 71 and 74 to be in a share of 22nd place, needed a strong final round today in Texas to advance to the final stage of qualifying.
Fox delivered a two-under par 70 to finish two shots outside of the qualifying mark - he needed to finish inside the top 18 players and ties to advance.
Fox had been one of the form Kiwi golfers on the PGA Tour of Australasia after winning the Western Australian Open and finishing inside the top-10 at the Perth Invitational.
Otago professional Thomas Campbell also missed out on the final stage of qualifying for the Web.Com Tour, finishing in a share of 45th. Wellington's Gareth Paddison and Waikato's Mathew Perry finished 66th and tied 68th respectively.