Yesterday's effort came thanks to a blistering start, with birdies on her first four holes. A bogey on five halted that run, but birdies on six and eight saw her card a first-nine 29. Two bogies blotted the scorecard coming home, but Ko rebounded to finish with consecutive birdies and hit an impressive 16 greens in regulations to sign for a 65 - the third-lowest round of the day.
Shadoff carded a 63 and Danielle Kang is a shot further back at 11-under, but with six shots separating the top seven, Ko is well poised for an excellent finish, though she may not be aware of it while on the course, due to avoiding glances at the leaderboard.
"I haven't done that the last two days or the whole of last week. I don't check the leaderboard very much anyway, even when I'm off the golf course – it's more Netflix for me," Ko said.
"Right now, score is a secondary thing, it's more important that I have belief in myself, and that I'm hitting every shot with confidence. That's the biggest goal – if I'm doing that and playing well on top of that, then I know things are clicking.
"It's more a fight against myself – believing in myself, and if I have those doubts, trying to overcome them. The more I get to play under these pressure conditions, the more I'll be able to assess myself and get better."
Ko also revealed she added seven pounds of muscle in the last two weeks, and credited Foley with helping her take her swing back to basics.
"Sean has been helping me to look a lot at my swings from when I was an amateur.
"Right now when I'm on the range I'm not really taking many swing videos, if the ball is doing what it's meant to do then there's no point in me over-analysing every little bit."
Ko isn't the only New Zealander at the top of world golfing leaderboards, with Steven Alker holding a share of the lead on the second-tier Korn Ferry Tour in the United States.
Alker, who led after the opening round in last week's event, now leads through two rounds at the Portland Open, with rounds of 68 and 65 placing him at nine-under.
On the European Tour, Ryan Fox sits in a share of 23rd at eight-under at the English Championship, six shots off the lead, after consecutive rounds of 67. Michael Campbell shot 70 and 73 to miss the cut.
Meanwhile, Danny Lee has made the cut at the PGA Championship - the fourth time Lee has made the cut at the major championship.
Lee carded four birdies and five bogies in a one-over round to drop to even par, sitting in tied 44th and making the cut by two strokes.
The lead is held by China's Haotong Li, at eight-under, two shots clear of a group of players which includes two-time defending champion Brooks Koepka, Justin Rose, Jason Day and Tommy Fleetwood.
