American Robert Streb and South African Retief Goosen set the pace as the world's best golfers went on a birdie blitz in the first round of the British Open at St Andrews.
Streb and Goosen each collected seven birdies to share the early clubhouse lead with six-under-par 66s on Thursday.
American stars Jordan Spieth and Dustin Johnson also moved to six under midway through their rounds as the Old Course was rendered defenceless on a still morning at the home of golf.
Chasing golf's fabled grand slam, Spieth made a lightning start with birdies on the first, second, fifth, sixth and seventh holes to make the turn in 31.
Three weeks after all but handing Spieth the US Open with a three-putt on the 72nd hole, Johnson matched the 21-year-old with five front-nine birdies of his own.
The playing partners continued their duel on the back nine, with Johnson adding a sixth birdie of the day on the par-4 10th and Spieth hitting back on the very next hole.
American amateur Jordan Niebrugge and compatriot Kevin Na were safely back in the clubhouse after signing for 67s, to trail Streb by a shot, while Australian Matt Jones and Englishman Greg Owen carded 68s.
Australian No.1 Jason Day was also travelling well at four under through 11 holes.
Earlier, little-known Swede David Lingmerth threatened to post the lowest score in British Open history after reaching the turn in just 29 shots.
Lingmerth, a winner on the US PGA tour at the Memorial Tournament in June, started his debut British Open on fire.
The Florida-based Swedish pro's blemish-free seven birdies before the turn matched Tony Jacklin's front-nine first-round record at St Andrews from 1970.
Only Denis Durham's 28 at Royal Birkdale in 1983 sits ahead of Lingmerth's efforts.
Unfortunately for Lingmerth, he let it slip on the back nine with three bogeys and an ugly double-bogey par-4 16th to finish with a three-under 69.
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