Charles Howell III played a bogey-free round as he shot a four-under-par 67 to hold a share of the lead at the Valspar Championship in Innisbrook.
Keegan Bradley and Ken Duke are tied with Howell after the opening round, one shot clear of Chesson Hadley.
"I was impressed I got away with no bogeys," Howell told reporters. "It was nice to get off to a good start here on a place like this. I'm not sure what the rest of the week will hold, but to actually play a nice round on a tough golf course is good for my confidence."
But it was a different story for world number one Jordan Spieth, who made five bogeys in his first seven holes and never recovered, carding a five-over 76.
Spieth now faces a tough task to make the cut and told PGATour,com: "I just didn't hit enough greens. I had the opportunities on a few holes today and actually there was a lot of holes where I thought if I hit great shots posing and it's 10, 15 yards off on the distance based on the gust of the wind.
"It was a very tough day. I got off to a poor start and I was behind the eight-ball with gusty wind on a tough golf course."
The three Irish competitors also had a difficult opening day.
Graeme McDowell bogeyed three of his last five holes for a three-over-par 74.
Padraig Harrington also shot 74 while Darren Clarke is six over par.
Charley Hoffman, Greg Yates and Chez Reavie lie two back of the leading trio on a leaderboard dominated by Americans. England's Danny Willett is one of 17 players four off the pace on one under.
Spieth later defended himself against an internet "troll" following his opening 76 in the Valspar Championship - and found an ally in one of his biggest rivals, Rory McIlroy.
Spieth said earlier this year that he had "gone away" from looking at comments on social media, but he could not resist responding to an Instagram user on Thursday night who wrote: "IF HIS PUTTER IS NOT WORKING, HES GARBAGE. Every other aspect of his game is very average."
The world number one, who is the defending champion at Innisbrook, replied: "Couldn't be further from the truth troll. Go do research before hating."
No, he's not TW, he's not slumping and he's not done. He's a double major winning 22 year old. He'll be just fine!! https://t.co/z0JHj72SiH
— Rory Mcilroy (@McIlroyRory) March 10, 2016
Spieth also took objection to a post on the PGA Tour's official Twitter account which had picked out a quote from his post-round interview in which the 22-year-old was asked if he could accept having an occasional off day.
"What good is kicking the door other than hurting my foot and (having to) withdraw?" Spieth joked at the time, although he was less happy to see the quote used in isolation.
"Seriously? That's the quote you're going to use out of that article?" he wrote on his own Twitter account.
Both the PGA Tour and Spieth have since deleted their tweets, but world number two Rory McIlroy was happy to leave up his response to a collection of some of the social media reaction to Spieth's round.
"No, he's not TW (Tiger Woods), he's not slumping and he's not done. He's a double major winning 22 year old. He'll be just fine!!" McIlroy wrote.
