After hitting his approach shot wide on the par-three eighth during the final round of The Open at St Andrews, the 21-year-old American putted off the green.
Yep, you read that right.
The unflappable Masters and US Open winner saw his monster putt roll off the green leaving him with an unlikely shot to save par.
Instead, he putted three more times for a double bogey five which dropped him to 12 under par and three off the lead.
With the top of the leaderboard stacked with talent, including Adam Scott, Sergio Garcia, Jason Day and 2010 Open winner Louis Oosthuizen, it'll be a long way back for Spieth. But you still wouldn't back against him too heavily to claw his way back.
Watch the video below to see Spieth's monster putt go horribly wrong.
Is this the moment #Spieth threw away a grand slam? #TheOpen pic.twitter.com/laR2Yr2iVx
— Brendan Bradford (@1bbradfo) July 20, 2015
And here's Spieth missing a relatively easy putt for bogey before throwing his ball away in disgust.
Jordan Spieth throws the ball away in frustration after the costly double bogey #theopen pic.twitter.com/5HoaiGIf6x
— Andrew Jerell Jones (@sluggahjells) July 20, 2015