(REUTERS) - Belgian Thomas Pieters rolled in a 31-foot birdie putt at the last to take the first-round lead with headliners Jordan Spieth and Rory McIlroy close behind at the World Golf Championship-Bridgestone Invitational on Thursday (Aug 3).
The 25-year-old Pieters, who began his round at the 10th, also chipped in for birdie at the first hole in a flawless five-under-par 65 at Firestone Country Club in Akron, Ohio, for a one-shot lead over Scotsman Russell Knox.
Spieth, showing no signs of a let-down following his British Open triumph two weeks ago at Royal Birkdale, was another shot back on three-under 67 along with four-time major winner McIlroy, playing alongside new caddie Harry Diamond.
The Northern Irishman split with his caddie of nine years, JP Fitzgerald, last week before the final WGC event of the season.
"It was good. A little weird at the start," McIlroy said about the new partnership with best friend Diamond.
"Obviously, it's been nine years since I've had anyone else on my bag."
Joining Spieth and McIlroy with 67s were double Masters winner Bubba Watson, Englishman Ross Fisher and American Kevin Kisner.
Another shot away was world number one Dustin Johnson, who crushed a 439-yard drive on his way to a birdie at the par-five 16th hole, and defending champion Jimmy Walker, who were among a group of six players to shoot two-under 68.