Shane Lowry carded a sweet 66 at the RBC Heritage to leave himself three off American leader Bud Cauley, who set a scorching opening-round pace in South Carolina.
Lowry birdied three of his last four holes to hoist himself up the leaderboard.
He headed for the clubhouse one off joint leaders Graham DeLaet and Luke Donald, but Cauley's flawless 63 nudged him ahead of the pack and into the outright lead.
What a finish!@BudCauley shoots 63 and leads by 2. #QuickHits pic.twitter.com/1GlQTzHjKH
— PGA TOUR (@PGATOUR) April 13, 2017
Donald continued his love affair with Harbour Town Golf Links as he posted an opening 65 to sit in a share of second place.
The Englishman has recorded six top-threes in his last eight appearances at the venue and he got off to a strong start on Thursday, carding an eagle, five birdies and a single bogey to get to six under par and lie in a tie for second with American Sam Saunders and Canadian Graham DeLaet.
Donald's fellow Englishman Ian Poulter was among the group a shot further back on five under alongside Lowry, Webb Simpson, Danny Lee, Russell Henley and Ben Crane.
Beginning his round at the 10th tee on Thursday morning, former world number one Donald rolled in a 15-foot birdie putt at his first hole before dropping his only shot of the day at the next.
After tapping in for another birdie at the 12th, Donald made back-to-back gains at the 17th and 18th to get to three under par at the turn.
The 39-year-old jumped to the top of the pile when he sank his eagle putt at the second after sending his approach to three feet.
Donald then picked up another shot at the fifth to move to six under before safely parring the final four holes to set the early clubhouse target.
In an interview screened on the PGA Tour's website, Donald said: "This place has been kind to me. It's nice to get off to a great start again.
"It's always nice to come back to places you feel comfortable and you've had success. Obviously I've had a lot of success here in the last eight years - I've done everything but win.
"It would be nice to give myself another chance to try and finally get over that hurdle."
Cauley reached the turn in 32 after making gains at the first, second, fifth and ninth.
The 27-year-old picked up another shot at the 14th before closing his round with three straight gains to finish the day on eight under.
DeLaet, meanwhile, made four birdies on his front nine before adding two further gains at the second and fourth, while Saunders birdied his last three holes to join Donald in a share of second.
