Jordan Spieth went on an epic run on the final five holes to win the British Open on Sunday, but it might never have happened if not for his caddie saving the day on the wild 13th hole.

At No. 13, Spieth hit his tee shot about 100 yards to the right of the fairway. After a nearly 15-minute delay, Spieth eventually decided to declare an unplayable lie and take a drop farther back on the practice range.

While Spieth had a much cleaner lie in the practice area, his shot to the green was blind, and his own calculation of how far he was from the green turned out to be way off. That's when caddie Michael Greller saved the day.

According to Spieth, he thought he was 270 yards to the front of the green, and he wanted to hit a 3-wood.

"I walked up there and tried to do the yardage in my head, and thought I was somewhere around 270 to the front, and Michael was like, 'Buddy, you're 230 to the front,' somewhere around there," Spieth said.

Spieth went on to say that normally he would trust his own yardage calculations on odd shots like that, but this time Greller expressed confidence in his own and Spieth relented.

"And Michael told me, 'No 3-wood — hit 3-iron,'" Spieth said. "If you asked me who has the better yardage, myself or Michael in a lot of situations, when we're on a crazy angle, I'd pick myself. And on that one he seems very confident. He was very adamant about what club to hit, and it gave me the confidence to hit it, because sometimes when that happens I'll still go with what I think. But he was right on."

Considering where Spieth was aiming, if he had hit the ball 30 to 40 yards farther, he would have ended up hitting the grandstand behind the green, at best, or landed in the long rough, at worst. Spieth would have been facing a double- or even triple-bogey and almost no shot of winning the tournament.

If Spieth had his way, his ball would have sailed well past the green. NBC Sports

Spieth did ultimately mishit the shot to the right. But thanks to Greller's yardage calculation, the ball still ended up in a good spot, just to the right of the green.

"After I struck it, I didn't like it because it wasn't where we were trying to hit it," Spieth said. "But I had some room, given the club I had and the yardage I had, which Michael was right on, fortunately."

Greller's work wasn't done when that hole was finished.

Spieth eventually bogeyed the hole, and for the first time all tournament he was no longer at the top of the leaderboard as he fell one stroke behind Matt Kuchar. But rather than feel the pressure, Greller convinced Spieth that the bogey save was actually a good thing, considering it could have been so much worse.

"When that putt went in, I was really, really obviously excited," Spieth said. "But I was walking off the green and Michael said, 'Hey.' He held me up, and he said, 'That's a momentum shift right there.' And he was dead on. And all I needed to do was believe that. I was starting to feel it ... Just his belief, when I know him so well, just fed over a bit. And all I needed was just a little bit of self-belief to be able to produce."