Justin Thomas' dad caddies for him in Round 3 at the Memorial Tournament

Justin Thomas said his caddie, Jimmy Johnson, began to feel dizzy and light-headed early on the back nine. He eventually had to be taken in, and this is one time it might have been a problem not to have spectators.

But his father and coach, Mike Thomas, has been following all week and stepped in for the last four-plus holes.

"I can tell he was light-headed and just didn't have a lot of energy," Thomas said. "I told him on 12 that if he needed to leave, he needed to leave. Just make sure he's OK, versus both of us worrying about it out there. I hit my tee shot (on 13) and Jimmy was gone and my dad was there."

Thomas three-putted the 15th for bogey, and then made double bogey on the 16th with a tee shot in the water. He shot 40 on the back nine and wound up with a 75.

Mike Thomas has faced tougher duties. He once filled in for Johnson two years ago on the Plantation Course at Kapalua, the course built on the side of a mountain, for the Sentry Tournament of Champions when Johnson injured his foot.

"That was a little harder walk," Mike Thomas said.