When it comes to the game of golf, Jordan Spieth has achieved what very few will ever have the opportunity to do.

The former world No.1 has won three majors, two Ryder Cups and boasts an impressive 13 wins on the PGA Tour.

Spieth has seen some incredible highs in the game of golf, all alongside his caddieGetty

And he has done it all with his longtime caddie behind him.

During his own long career of carrying the bag for Spieth – beginning back in 2011 – Michael Greller has shared in those incredible highs.

But he has also witnessed some of the lows.

While there’s no doubt that Spieth has had a Hall of Fame career, that doesn’t come without a fair share of tough losses.

Speaking recently, Greller was asked if one mistake sticks out in his time as a caddie, and quickly cast his mind back to the 2015 Open Championship at St Andrews.

“For me, that was the hardest loss,” he began.

“A caddie once told me, the better a player you work for the more great wins you’re going to have, and the more tough losses you’re going to have.

“You want to work for the greats, and you’re going to have those tough losses.

“St Andrews, that was a tough one because [Spieth] had won the first two majors that year and he was tied for the lead with two holes to go.”

On that day, the US star had a chance to win his third major of the season but failed to birdie either of the final two holes to earn a spot in a playoff.

Spieth’s caddie has shared his biggest regretGetty

The moment that stings Greller the most came on hole 18 when Spieth came up short with his approach, leaving himself with an an impossible birdie putt.

“If I had to re-do, he ended up hitting a gap wedge, he was left and he was being aggressive because he was trying to make birdie there on the 18th hole at St Andrews,” Greller recalled.

“And he ended up coming up short and it came all the way back down to the bottom, and he had to make a 40-footer to get in the playoff.”

Greller went on to reveal just how upset that moment made him.

“I actually cried after that one I was so upset,” he said.

“It was just he was on the cusp of having a great chance to literally win the first three majors.

Spieth won the US Open Championship in 2015

“Then he ended up getting solo-second at Whistling Straits that year at the PGA [Championship].

“He was not far off from winning all four majors So that’s probably one that I think about.”