Unflappable Dustin Johnson has fired his equal-lowest round at a major to seize the outright British Open lead.

Johnson’s sizzling seven-under-par 65 earned the world No.4 a one-stroke buffer on a jam-packed and star-studded leaderboard on Thursday.

Fellow Americans Zach Johnson and Robert Streb, Australian Jason Day, South African Retief Goosen and Scotland’s 1999 champion Paul Lawrie share second spot as the world’s best golfers tamed the famous Old Course on the opening day.

Chasing the fabled grand slam, Masters and US Open champion Jordan Spieth is among five players two shots adrift after signing for a five-under 67.

But barring a late surge from one of the late-afternoon starters, Johnson will hold the first-round lead for the second straight major after the 31-year-old shared top spot with Henrik Stenson last month at Chambers Bay.

“I played really solidly today. I drove it well, I drove it straight,” Johnson said after accruing five birdies and an eagle on the 521-metre par-five fifth.

“This venue here is one of my favourite Opens. It’s kind of hard to beat St Andrews for an Open Championship.

“I really like the golf course. I think it sets up well for me.”

Johnson also carded a brilliant opening 65 at Chambers Bay, only to three-putt the 72nd hole on Sunday to all but hand Spieth the trophy.

But not looking back, the laid-back Johnson insisted he wasn’t eyeing redemption at the spiritual home of golf.

“I’ve said a bunch of times: nothing bad happened at Chambers Bay. I wasn’t disappointed, really,” he said.

“I played really well, did everything I was supposed to. I couldn’t control what the ball was doing on the greens there.

“There’s really no bad feelings from that, only good. I played really well and then it carried over to today.”

Playing alongside Johnson, Spieth went shot-for-shot with the big-hitting challenger on the front nine as the marquee pair each went out in 31.

Spieth, though, dropped shots at the 13th and 17th before closing with a birdie on 18.

“I was able to take advantage on the front nine and then turned into the back nine and was just able to hang on,” Spieth said.

“Even par was a good score on the back nine.”

American amateur Jordan Niebrugge, compatriots Kevin Na and Zach Johnson, South African major winners Charl Schwarzel and Louis Oosthuizen, the last champion at St Andrews in 2010, are all also at five-under with Spieth.

Australian Matt Jones is among a bunch of players one stroke further adrift after carding a solid 68.

All up, 52 players – exactly a third of the field – were in red figures late in the opening round.

Little-known Swede David Lingmerth is three under but threatened to post the lowest score in Open history after reaching the turn in 29.

A winner on the US PGA tour at the Memorial Tournament in June, Lingmerth’s outward total matched Tony Jacklin’s first-round front-nine record at St Andrews, set way back in 1970.

But Tiger Woods faces an almighty battle to make the halfway cut after opening with a nightmare four-over 76, his worst-ever round as a professional at St Andrews – where the 14-times major winner raised the Claret Jug in 2000 and 2005.