After sitting at even par through the turn, three bogies and a double bogey saw the world No5 tumble down the leaderboard, and extended her drought to seven straight tournaments without a top-10 finish.
Such a streak is commonplace for most, but it comes after Ko had accrued seven top-10 finishes in her previous 10 tournaments, while her missed cut is the third of her 2017 season.
Scenes were similar for New Zealand's other leading golfer, Danny Lee, on the PGA Tour.
Lee carded rounds of 74 and 71 to miss the cut by three shots at the Northern Trust; a tournament which doubles as the first event of the PGA Tour playoffs.
The tournament is led by three of the world's best golfers, with Jordan Spieth, Rickie Fowler and Dustin Johnson sharing the lead at six-under, alongside Colombian Jhonattan Vegas.
The top 100 golfers in the year-long FedEx Cup rankings qualify for next week's event, and despite the missed cut, Lee sits 65th and will tee up next weekend at the Dell Technologies Championship.
After that event, the field contracts again, with the top 70 players making the penultimate event, and the top 30 qualifying for the season-ending decider.
The winner of the overall playoffs will come away with US$10 million ($13.8 million).