Spieth made nine consecutive pars before finally breaking the streak with a birdie at the par-5 11th.
“Once the one on (No.) 11 went, even though it was a simple up and down, I at least saw another birdie go,” Spieth said.
And after another birdie at the 12th, “we were off to the races,” he said.
“The holes started to look bigger. A lot of times it just takes one to go for me to really find that extra confidence, that extra little pop in my stroke,” Spieth said.
“And on the back nine it was nice to get in the zone. The holes that I didn't birdie, 10 just barely missed … 14 was short in the heart. And then 15 was a great two-putt. So, yeah, very, very pleased to have a chance to win another major.”
Spieth, who shot 6-under 30 on the back nine for a 7-under 65 total, will play in the final twosome on Sunday at Whistling Straits. He trails leader Jason Day by two strokes in his bid to join Ben Hogan (1953) and Tiger Woods (2000) as the only men to win three professional majors in a single season.
It could have been a much more arduous task if not for his caddie. As Spieth lagged behind a field on a birdie-happy course, Michael Greller implored patience. And his boss responded.
“I think it's something that me and Michael, we both learned from past major championship weekends. I wasn't thinking as much on Thursday as I was thinking about how in the tournaments, in the majors that we've won, the putts have fallen on the weekend just strictly by just letting it happen. Giving yourself opportunities, believing that it will fall – being stubborn on the greens, is what Michael likes to say,” Spieth said.
“So I would drawback on past major weekends as a different type of experience than any other experience that you can have. And luckily that hole looks big recently for us on major weekends, and that's what we just had to keep believing today.”