Day was rolling along at four-under par in his second round and nine under on the week when a double-bogey at the par-five 15th, where his third shot from a severe downslope found the pond that fronts the green.
The Australian followed that with bogeys at the 16th and 18th holes, and while he remains in the mix he is well aware that he could be much closer to clubhouse leader Brooks Koepka (32) going into what is expected to be a rain-filled weekend.
"Yeah, I'm actually very disappointed with how I finished," said Day.
"Being decently close to where Brooks was going into the weekend, you never know how it goes, and obviously going from 9 (under par) to 5 (under) was a bit of a kick in the gut."
Day was considered a contender coming into the year's first major a given a return to form that has produced five top-10 finishes in seven events this year and Friday's even-par 72 brought him to five under on the week, seven back of Koepka.
Despite the late errors, Day was able to take some comfort in the overall state of his game, which has shown great strides since he slid down the rankings due to a mix of back issues, swing changes and putting woes.
"It feels good, but today kind of ruins it for me," Day said with a laugh. "I've just got to give myself time.
"I've just got off the golf course and I'm thoroughly annoyed with myself, and I'm sitting here answering questions, and that can be difficult because it's in the heat of the moment, and I'm trying to get a hold of myself."
The highlight of Day's second round came at the par-four 11th where he missed the green with his approach shot but managed to chip in for birdie from 22 yards.
Day said seeing his ball drop did not make him recall Larry Mize's miraculous chip-in on the same hole to defeat Australian Greg Norman in a playoff in the 1987 Masters.
"No, actually to be honest I was trying to just get it up-and-down, and fortunately I hit a really nice chip shot, and it went in, which was good," said Day.
"That was kind of the nice kick in the right direction going off on the back side that I needed just because I wasn't hitting it as good as yesterday.
"Sometimes you need things like that to go your way."
