Was the world's No. 1 player offering an impromptu pep talk to the Masters champion? Was he employing a little trash-talking inside the ropes?
"We were talking about hairstyles," a smiling McIlroy later said. "I sort of said to him, 'You have a green jacket, your hair can be whatever you want it to be.'"
Paired together for just the seventh round in their young careers, McIlroy opened his Players Championship campaign with a 3-under 69 while Spieth struggled to a 75.
"Just didn't quite trust it today until I was already too far behind the 8-ball," Spieth said. "Just a really, really poor day. I've got to find something to work on. Sometimes when you're hitting it really well, you just get tough breaks and you have a bad day. This wasn't one of those. I actually really need to find something on the range."
He added that it was his flatstick that kept his score in the 70s.
"If I didn't putt well today," he said, "it could have gone up there towards that 8 number."
Meanwhile, it was business as usual for McIlroy.
Fresh off his WGC-Cadillac Match Play victory last weekend, he posted an eagle and two birdies against a lone bogey on a TPC Sawgrass course he described as "frustrating" one day earlier.
"I've learned now what a good score is around this golf course," he said of his Players experiences. "I think anything in the 60s is a decent score today. Anything under par, really."
Playing the back nine first, McIlroy raced out to a 3-under 33 on that side, his fifth consecutive back-nine split of 33 or better on this course, dating back to last year. He closed with an even-par 36 on the front.
"There's a lot of chances on that back nine," he said. "I just feel comfortable on it, feel comfortable on the closing stretch, so if I can keep up my good play on back nine like I have and be a little bit more consistent like I was on the front nine, then hopefully that bodes well for the week."
The third member of their group, seventh-ranked Jason Day, also opened with a 69.
McIlroy pleased, Spieth struggles
Rory McIlroy and Jordan Spieth discuss their first-round performance in the Players Championship.