Mickelson, who produced a stunning display yesterday, falling one short of a record major round, survived tough conditions on his way to finishing on two-under-par for the day.

Sweden's Stenson shot an excellent six-under-par to close the gap on the American and boost his chances of a maiden major success.

The 40-year-old's best finish on one of golf's four annual flagship tournaments came at The Open in 2013, where he finished second behind Mickelson.

Denmark's Soren Kjeldsen and American Keegan Bradley remain in contention as they are both three off the lead on seven-under-par, two shots in front of defending champion Zach Johnson of the US.

Rory McIlroy of Northern Ireland, who made the headlines in the build-up to the competition when he claimed the Olympic golf tournament "didn't matter", played through the worst weather which befell the Scottish course but ended day two on a respectable two-under.

Patrick Reed of the US was unable to build on his performance yesterday as he carded a three-over 74 to join McIlroy and five other players in joint 15th position on the leaderboard.

World number three Jordan Spieth and England's Danny Willett, winner of this year's Masters, are likely to just about make the cut, which is projected to be four-over-par.

"If I look back to my mid-30s, I am 35lbs lighter, in better shape than I was and can manage the symptoms of my psoriatic arthritis," Mickelson told the BBC.

"I feel stronger and in a better condition than I have ever been.

"I can't see why I can't play my best golf in the coming years. 

"I am optimistic about this week and the coming years and the opportunities to add to my resume."