Hideki Matsuyama admitted the pressure of being in contention at the US PGA Championship got to him during the third round.
The world number three carded a two-over 73 at Quail Hollow on Saturday, but he is just a shot off the lead.
Matsuyama, 25, said the pressure of sharing the overnight lead may have had an impact as he bids to become the first Japanese player to win a major.
"Probably the pressure had something to do with it, being in the last group of a major tournament," he said through a translator.
"But I haven't been spot on all week. And the worries that I had about my swing showed up today in the way I played."
Matsuyama had played down his second round, a brilliant seven-under 64 that saw him surge into contention.
But he ended up hitting just eight fairways in his third round, making it a challenging day.
"I'm disappointed the way I played today," Matsuyama said.
"However, I'm happy to just to be one stroke back and still have a chance and looking forward to tomorrow."
Matsuyama is tied for second with Chris Stroud (71) as the duo chase Kevin Kisner (72).
Stroud, who only made the field thanks to his first PGA Tour win at the Barracuda Championship last week, is upbeat heading into the final round.
"In college, my nickname was Mr. Positivity. It carried on playing golf," he said.
"It definitely helped me early on in my career, just overcoming some very difficult situations: Getting through first and second stage of Q-School, getting on Tour in 2007.
"Been out here, I think this is my 11th season. To finally get a win is really magical. I'm still on cloud nine. I'm just enjoying it."