Phil Mickelson has taken early command of the British Open with a spectacular record-equalling first-round 63 at Royal Troon.

Steven Alker is the best of the Kiwis on two over par with Danny Lee blowing out to a seven over 79.

Mickelson - the 2013 Open winner - lipped out for birdie on the final hole just as he seemed poised to record the lowest round in major championship history.

Mickelson's magical eight-under display was still a course record and matched the best-ever score at a major.

The five-times major champion enjoys a three-stroke advantage over countryman Patrick Reed, with fellow Americans Justin Thomas, Steve Stricker, Tony Finau and Billy Horschel among a bunch of players a further shot back.

Englishman Andy Sullivan and Soren Kjeldsen also carded 67s, but the day undoubtedly belonged to Mickelson, who was flawless in his eight-birdie round.

The back nine at Troon is one of the toughest homeward stretches on the Open rota, but the flamboyant left-hander made a mockery of its beastly reputation with just 31 shots after the turn.

Bidding to become the oldest Open winner since Old Tom Morris in 1867, the 46-year-old said only his final-round 66 to seal victory three years ago could top Thursday's effort.

"It was one of the best rounds that I've played," Mickelson said.

"I mean, nothing will match that final round at Muirfield, but it was one of the best rounds I've ever played and I was able to take advantage of these conditions - and yet I want to shed a tear right now.

"That putt on 18 was an opportunity to do something historical. I knew it, and with a foot to go I thought I had done it.

"I saw that ball rolling right in the centre. I went to go get it, I had that surge of adrenaline that I had just shot 62 - and then I had the heartbreak that I didn't and watched that ball lip out.

"It was, wow, that stings."

Reed had birdied the last hole to seize the early clubhouse lead as Americans once again dominate the Open at Troon.

Aided by a hole-out eagle from the third fairway, Reed led for most of the afternoon.

Americans have provided the past six Open winners at Troon, stretching back to Arnold Palmer in 1962 and are once again threatening to continue the 54-year streak.

Mickelson's brilliance has left Jason Day facing a mountain to climb to work his way back into the tournament after Australia's world No.1 disappointed with a two-over 73.