Patrick Reed led another strong American challenge with a record opening round in The Open at Royal Troon and Rory McIlroy was left to rue a double-bogey which leaves him three shots off the pace.
The last six editions of golf's oldest major contested at Troon were won by Americans and Texan Reed shot a lowest-ever first round of 66 in an Open at the famous South Ayrshire course to go in front on his own on five under.
Reed made an eagle at the third, as well as five birdies under blue skies on Thursday to put himself into early contention to win a first major.
Fellow-American Justin Thomas had set the clubhouse target with a 67, while compatriots Steve Stricker and Billy Horschel are also four under after their first rounds.
Open debutant Thomas birdied the first four holes in an impressive start, but a double-bogey at the 15th cost him the outright lead, while Stricker came up with three birdies in the last five holes despite the back nine being far more demanding.
Horschel - one of a small number of players to break par on the back nine - dropped only one shot at the third as the North Americans made their presence felt once again.
Justin Rose is well poised after starting with a three-under 68, with the only blemish on the Englishman's card coming when he dropped a shot at the seventh.
McIlroy paid the price for a two-putt at 13, where the three-time major champion dropped a couple of shots and also bogeyed the next as the top players in the world were tested after the turn.
Two-time major-winner Jordan Spieth had to settle for level-par, finishing with a third bogey following a stray tee shot which sailed way out to the right at 18.
World number one Jason Day has work to do, with the Australian making only two birdies to sit seven shots adrift of Reed on two over.
Defending champion Zach Johnson started with back-to-back birdies, while U.S. Open champion Dustin Johnson bogeyed his first hole.