An hour after sunrise Thursday morning, defending FedEx Cup champion Rory McIlroy crouched in an ice bath with minimal confidence his ailing back would awaken in time for the opening round of the Tour Championship a few hours later.

But the Northern Irishman more than survived with an opening-round 70 and hopes to be closer to healthy by the time he tees up Friday.

McIlroy said there was no chance he wouldn't be on tee box Thursday and has no plans to withdraw even if pain returns.

He's 7 under par, three shots behind leaders Collin Morikawa, Keegan Bradley and Viktor Hovland of Norway. His most important second-round prep started soon after turning in his scorecard; treatment overnight is on his agenda.

McIlroy sounds more confident his back will cooperate for the final 72 holes at East Lake Golf Club in Atlanta, which was very much in doubt 24 hours earlier.

"On Tuesday morning, I felt a little tight. I went into my gym at home, and I just sort of foam-rolled and stretched," McIlroy said Thursday. "I went to grab something, and my whole right side just completely seized up, spasm. So I spent two hours with the physio at home, flew up (to Atlanta), felt a little better, some treatment."

On Wednesday morning, McIlroy said his right side was "feeling better" and he went to the gym.

"I was at the bottom of a squat, a body-weight squat, and my whole lower back spasmed, seized up. I couldn't move," he said Thursday. "I honestly couldn't address the ball this time (Wednesday). So to get to where I am today is good."

McIlroy managed to hit just 20 golf balls at the range in preparation for Thursday's round. At 2 over through nine holes, McIlroy said he still felt confident in his ability to navigate the course. He birdied four holes and finished 2 under on the back nine.

McIlroy, 34, is the only three-time FedEx Cup champion in history, having won the season-long title in 2016, 2019 and 2022. He beat out Scottie Scheffler in a final-round comeback at the Tour Championship last year.

He started the week in third place at 7 under par as part of the event's "staggered start" based on FedEx Cup points. Scottie Scheffler and Hovland were first and second at 10 and 8 under, respectively. Scheffler now sits in fourth at 9 under after opening with a 71.