The Open - Henrik Stenson grabs one-shot lead over Phil Mickelson as final day duel looms at Troon

Sweden's Stenson, seeking his first major at the age of 40, shot a third round 68 - the joint-best of the day - to move to 12 under par, a shot ahead of Mickelson.

The American veteran, seeking a sixth major championship title but his first since the 2013 Open at Muirfield, fired a 70 to keep pace with the Swede.

The rest of the field seems out of it: Bill Haas, at -6 after a third round 69, is the nearest challenger some five shots distant.

Tournaments, and indeed majors, have been won from further back; Paul Lawrie was 10 shots off the lead ahead of the final round at Carnoustie in 1999.

Such turnarounds are stunningly rare, though the Masters this year witnessed just such a surprise as Jordan Spieth collapsed on the final day at Augusta having led by five.

One man whom the crowd would love to see such heroics from is the player who will partner Haas in the penultimate group on Sunday: that man is Andrew 'Beef' Johnston, the English journeyman who has become a huge hit with the crowds for his affable demeanour on the links.

JB Holmes is a shot further back at -4, before a group of three at -3 and one of four on -2 that includes Sergio Garcia - but there seems little prospect of anyone except the leading duo battling for the title on Sunday.

One thing is certain: neither Rory McIlroy nor Jason Day nor Jordan Spieth will challenge for the Claret Jug in the final round, being 12, 13 and 17 shots respectively off the lead. US Open champion Dustin Johnson is the only one of golf's new big four who enters the final day under par - but at -1, he too is out of contention barring a historic collapse from both the front-runners.

Stenson roared ahead of overnight leader Mickelson early on as he birdied three of the opening four holes on Saturday.

Mickelson, who beat Stenson into runners-up spot in this tournament at Muirfield three years ago, made one early birdie to try and keep pace with his nearest challenger.

And it was the ageing American, a winner of five major titles, who went back into the lead as Stenson dropped shots at the 6th and 8th holes to fall back to -10, a shot behind Mickelson.

Mickelson then pulled a further shot ahead with a birdie on the 13th - only for Stenson to level on the next with a brilliant tee shot to set up a birdie, while Mickelson missed a two-foot putt for par - a two-shot swing which switched the momentum around.

Stenson then added another birdie on the par-3 17th hole to edge into the lead, and both players parred the last to ensure that it would be the Swede who leads into the final round.

"Hopefully it'll all be good enough when we add it all up tomorrow," said Stenson.

"I've got two thirds and a second - I know what I want to get out of this week," he added, referring to his near-misses in the past.

Mickelson was sanguine about his efforts, saying that he merely "found a way to get the ball in the hole" throughout.

"It could have been a round that got away from me a little but it didn't," he said, "instead I shot under par...

"You just have to shoot a number, it doesn't matter how...

"It's a great opportunity, a great challenge," he added.

"Henrik's playing really good golf, so I'm going to have to go and shoot a really good number."

Bradley Keegan reached -6 at one point while Soren Kjeldsen of Denmark got to -7, but both dropped shots on Troon's fearsome back nine to slip to -3 and -2 respectively.

McIlroy posted a two-over-par round of 73 to leave him level par - but on a frustrating day when he missed several good chances his 'highlight' came as he threw his 3-wood away on the 16th, an act which saw him break his club in half.

With conditions tough the only player to make a significant move on the leaderboard was Steve Stricker, with a joint best round of the day three-under-par 68 by to finish at -3.

That score of 68 was also recorded by Brandt Snedeker and Haydn Porteous, but both are too far back to challenge. Then again, the entire field apart from the leading two has very little chance of overhauling either Mickelson or Stenson on what promises to be a thrilling Sunday duel at The Open.