PGA Tour rookie Shawn Stefani grabbed a two-shot lead after a tricky opening round of the Tampa Bay Championship on Thursday.

On a difficult day for low scoring on the Copperhead layout at Innisbrook Resort, the American carded a bogey-free round of six-under-par 65.

Fellow American Brian Harman, playing the back nine first, bogeyed his final hole to spoil an otherwise flawless round, settling for a 67 and outright second place.

Tag Ridings birdied his last two holes to join Brendan Steele and Harris English in a three-way tie for third at three-under on a day when only 25 players among the 156 starters broke par.

English might have finished higher but made a double bogey on his last hole when he found a greenside bunker, then three-putted.

Former world number one Vijay Singh of Fiji was among a group of eight players who finished at two-under, while last year's champion, Luke Donald, signed for a one-under 70 despite bogeys on three of his last four holes.

"I'm extremely disappointed right now. I played just lovely golf for 16 of the 18 holes today," Donald said.

"I just had it really under control and could have been six or seven under with a couple of putts and obviously to finish like that, it leaves a bitter taste in my mouth."

Stefani, who won twice on the Web.com Tour last year, made a strong start in the unseasonable chilly Florida weather and strong winds, with three birdies in his first five holes after teeing off at the 10th.

The 31-year-old also birdied three of the first five holes on the back nine, then safely parred the last four to lead a PGA Tour event for the first time.

"I stayed patient all day," he said. "I kind of fought through some not-so-good shots toward the end of the day. It all worked out." (Reporting by Julian Linden; Editing by Mark Lamport-Stokes)