What is the deal for tomorrow's action in the PGA Championship?
Playing in Saturday's final group with Kisner and Matsuyama, Day's nightmare round was epitomised by a weird decision on the par-four 18th hole to go for the green with his approach after finding trouble from the tee.
Day declined to speak to reporters as he left the clubhouse following an anything-but-boring back nine that included three birdies, two bogeys, a double bogey and that eight on the 18th.
On undulating greens, some of the hole locations were extremely hard, with nobody on the leaderboard shooting better than the 68 by Canadian Graham DeLaet, who went six-under in a remarkable four-hole stretch to vault within five strokes of the lead. Thomas bogeyed three of his first five holes, Koepka birdied his first two and, well, that was that.
The Australian started the 18th hole four shots off the lead but hit his first short close behind a tree.
Marc Leishman had an even-par 71 highlighted by an eagle at the par-five 10th hole. On the final hole, he hit right, onto loose straw behind a tree.
His tee shot on No. 10 went off to the right of the fairway. It did not work. Instead, it's going to take a miracle for him to catch Kisner.
Starting the proceedings at six-under, Day even went to seven-under with a birdie, but by the time the front nine ended, he was five-under. "I really haven't had the greatest year, '" he said prior to the opening round. "It's unfortunate. He played good coming in and then gave it all away, so that's tough".More news: Keith Ellison: 'Irresponsible' Trump could bring about first strike by North Korea
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Kisner was not watching Day carefully because he had his own problems. He has a one-stroke lead. "I dropped it in a pretty bad lie, so I couldn't carry it over the cart path".
"I'm just excited about the opportunity". I wasn't too concerned with watching Jason. And there's a lot of putts that honestly, I'm not trying to make.
Kisner finished one shot ahead of Hideki Matsuyama and fellow American Chris Stroud after a round of 72. He credits a new attitude, in which he stopped pressuring himself for victories. "I'm as relaxed as I've ever been".
"This is my first experience leading a major, or tied for the lead after 36 holes".
However, last week's WGC Invitational victor Hideki Matsuyama was threatening to challenge Kisner's supremacy before a weather delay halted him in his tracks. "And the worries that I had about my swing showed up today in the way I played".
The build-up to this year's event was heavily focussed on McIlroy and Spieth with the Northern Ireland player favourite at Quail Hollow - where he holds the course record - and the American bidding to beat that record held by compatriot Woods.
"However, I'm happy to just be one stroke back and still have a chance", he said.