Jordan Spieth goes from 3-under to 1-over in four holes

CARNOUSTIE, Scotland -- Jordan Spieth put his nightmare first-round finish at The Open down to a combination of a "brain fart" and falling back to the type of golf he is trying to steer himself away from as he seeks to regain his best form.

But despite carding a 72 -- 1 over and 6 shots off first-round leader Kevin Kisner -- he is adamant he can still defend his title if he improves his execution.

It looked like such a promising round for Spieth, who was 3 under par as he teed off on the 15th, but he hit his opening effort into the fescue and then plugged his next shot in the most troublesome pot bunker on the hole. He went on to double-bogey the 15th and bogeyed two of the final three holes, having found the Barry Burn on the 18th.

Talking about his aberration on the 15th, he put it down to a "brain fart," saying his second shot was a "really, really poor decision." And as he assessed his round afterward, he said it felt like a "missed opportunity," as it brought an end to his streak of five straight rounds in the 60s at The Open, and his first over-par first round at this competition.

"I felt like I was really going well," Spieth said. "I had a nice par save after driving it in the bunker at 6. Other than that, it was very stress-free. I was putting the ball where I needed to, having maybe no more than four feet for par on every hole. It was just a clean round of golf. I've done a bit of that this year, just the decision making that's cost me.

"But the misses toward the end were the exact misses that I've been having and I'm working away from. My swing just didn't quite hold up to the end of my round. Those long irons really hurt me today."