William McGirt and Mackenzie Hughes upstaged a star-studded Players Championship field to earn a share of the lead after the opening round. "It paid off", said Hughes, who already has won (Sea Island) in his rookie season on the PGA Tour.
American McGirt and Canadian Hughes will take a one-shot lead into day two of golf's unofficial fifth major, with JB Holmes, Chez Reavie, Jon Rahm and Alex Noren (68) trailing in third at four under.
Defending champion Jason Day is only three shots out of the lead after a 2-under 70 day.
He told reporters: "I've been struggling with it a bit this week, and I sort of felt it for the first time on Sunday".
McIlroy's injury is a recurrence of the back and rib problem which kept him out for seven weeks at the start of the season, although he was able to add a 71 to his opening 73 to finish level par alongside Masters champion Sergio Garcia and world number one Dustin Johnson.
"I've played here 25 years, so it's not like that one round was going to make a big difference", Mickelson said.
Adam Scott, of Australia, hits from the second tee during the first round of The Players Championship golf tournament Thursday, May 11, 2017, in Ponte Vedra Beach, Fla.
Alex Noren, a four-time victor on the European Tour last season, bogeyed the last for a 72 and the Swede will go into the final round alongside Garcia on five under, while Francesco Molinari (69) and Garcia's compatriot Rafa Cabrera Bello (73) are a further shot adrift.
"It's hard to stay out of trouble all day and it just depends where you want to get into trouble", said Scott, who was 6-under through 16 holes but doused his tee shot at No. 17 and his second shot at No. 18 into the water to set up double bogeys.
"So just working on that, as I said, but the warm weather helps, it helps it stay a little looser". So it's, it might just be a flare-up of what happened previously and I just need to rest for a few days and it might be OK.
"The feeling was great", he said.
And Garcia managed a 73 with the eighth ace on the island-green 17th hole in Players Championship history and a tough par save on the 18th. "Overall it was okay; I can't believe I'm only five off the lead and I can go out tomorrow morning, hopefully post a good score and get myself right back into the tournament". He posted the tournament 72-hole record that year, 24-under-par-264. "A few distractions earlier this year kind of derailed that a little bit which is understandable, I had to be there with my mum, and now I'm ready to focus on my golf".
He made it sound simple, even though the Players Stadium Course can be anything but that.
"Obviously, it could have been really good today but ended up just being okay". "And then I went back at it on Friday and instead of maybe gradually building it up again, I hit balls for four or five hours on Friday and did the same on Saturday".