Stenson started the day a shot behind Mickelson, but his three-under-par round of 68 was two better than that of his rival and puts him top of the leaderboard on 12 under. 

"I've always thought it's better to be one ahead than one behind," Stenson, who is bidding to become the first Scandinavian to win a major title, told the BBC.

"I know Phil's not going to back down, and I'm certainly not going to back down either.

"Even though Phil's popular in this part of the world, maybe I'll have a few more Europeans giving me a push and we can get a Ryder Cup atmosphere going."

American Bill Haas is a distant third on six under after a 69, one ahead of England’s Andrew Johnston, who posted 70.

JB Holmes is fifth on four under after also scoring 69, and is one ahead of fellow Americans Steve Stricker and Tony Finau, and Denmark's Soren Kjeldsen.

Northern Ireland’s Rory McIlroy finished on level par after a 73, while world number one Jason Day of Australia is one-over-par following a 71.

World number three Jordan Spieth is five over after a 72, the same round carded by fellow American Dustin Johnson who is better placed on one under.

Despite being one shot off the pace at the halfway stage, Stenson found himself one shot in front on 12 under following birdies on the third and fourth holes.

The 40-year-old bogeyed the sixth and the eighth though to give the lead back to Mickelson, who registered nine consecutive pars between the fourth and 12th.

A birdie at the par-four 13th saw Mickelson move two clear, but he then bogeyed the par-three 15th, which Stenson holed in two to tie for the lead.

Mickelson managed a birdie four at the long 16th, but he gave the shot straight back when he missed the 17th green to the left and Stenson regained the lead with a 15-foot putt.

Stenson pulled his approach to the 18^th after Mickelson had found sand, but their reliable short-games salvaged a pair of pars and set up what promises to be a thrilling duel over the Old Course tomorrow. 

If Mickelson triumphs, he would be the seventh American in a row to win The Open at Royal Troon.

"I have to get my rhythm back," said the 46-year-old, who is chasing his second Open win, having beaten Stenson into second place in 2013 at Muirfield.

"My rhythm was out of sorts.

"I shot under par and kept myself right in it but I'd love to play the final round like I played the first two and give myself a shot.

"Hopefully I get dialled back in."