Former PGA Championship winner Keegan Bradley rattled off four birdies from the last five holes to open up a two-shot lead on the opening day of the Valspar Championship at Palm Harbor on Thursday.

The 34-year-old American, who is currently ranked 63rd, missed only one green on a day of low scoring as he carded a seven-under 64.

Bradley hit two birdies on the front nine, before accelerating on the back nine with five birdies from his final seven holes to claim a good lead ahead of five players tied in second.

"I know that I'm going to have some bogeys and some stress coming," Bradley said. "But as for today, I played so good and it feels good to go around a course like this and shoot that score."

Argentina's Emiliano Grillo along with American quartet Ryan Moore, Hank Lebioda, Max Homa and Patton Kizzire finished with five-under 66s to sit behind Bradley on the leaderboard.

World number two Justin Thomas is five back after a two-under 69 despite an eagle on the first, with three bogeys slowing him up.

Top ranked Dustin Johnson finished the opening day further back with an even 71, where he had a mixed front nine with three birdies and two bogeys, while Phil Mickelson shot 73 to start.