As the duo headed down the stretch, it was natural to wonder if Stenson - having never been in this position before, though he did finish runner-up to Mickelson at the 2013 Open - might let the tension get to him.
They matched pars on only six of the 18 holes. Momentum could change with any shot.
The British Open ambitions of Dustin Johnson and Rickie Fowler were derailed at "The Railway" 11th hole.
Henrik Stenson and Phil Mickelson are locked in a memorable duel at Royal Troon.
Lefty's 25-foot birdie putt on the 13th hole gave him a two-shot lead. There's only one thing that matters tomorrow. "As we know it's going to take some good golfing to do that, but I'm certainly willing to give it a try", Stenson said. So it should be an exciting afternoon.
Links golf can deliver some odd finishes, though this had all the trappings of a two-man race today. Starting a shot behind Stenson, he took the lead on the first hole when his birdie topped Stenson's bogey.
Henrik Stenson of Sweden plays his tee shit from the12th during the final round of the British Open Golf Championship at the Royal Troon Golf Club in Troon, Scotland, Sunday, July 17, 2016.
Mickelson, winless since he lifted golf's oldest trophy at Muirfield three years ago, had a 70.
Stenson played such a ideal round that he putted for birdie on every hole, three-putting from 80 just off the first green and three-putting from 40 feet on No. 11.
It looks like there could be some low scores before the day is done. "But either way, I shot three rounds under par". He made an 18-foot putt at the 14th, and putting from off the green at 15, Stenson drained a roll of 51 feet.
Stenson couldn't sustain the onslaught with two bogeys to turn in 35, as did Mickelson with that one birdie - Mickelson led by a shot at 11-under.
The Swede stands at 12-under 201, a lead of one shot from Mickelson, after an excellent third-round score of 68 in cool and blustery conditions on Scotland's west coast on Saturday.
Everyone else felt like mere spectators. Another shot back was Andrew Johnston, the Englishman with a big belly and beard to match who goes by "Beef". Jason Day has managed to stay at 2-under-par for the day through 14th.
It was unlikely to matter.
But Stenson also equaled the record for low round in any major with a 63, and he did it on Sunday, when it mattered most.
The 40-year-old becomes the first Scandinavian player to win a major title, and he was only the second in history to fire a final-day 63 to do so - emulating the feat of Johnny Miller when he stormed to the US Open title at Oakmont in 1973.
The Swede, who had never won a major before, started the day at Royal Troon one shot ahead of Phil Mickelson. He posted a 6-under 65, which was good for his lowest final round in a major.
KEY STATISTIC: Stenson and Mickelson had a better-ball score of 59 in the final group. He hasn't won another tournament since, and at age 46, it appeared time was running out. We played at Augusta, we played at the US Open.
He has the chance to make up for Muirfield and finally be a victor after seven top-four finishes in majors.
The 2014 champion had a two-over 73 to fall to even-par and his frustration was summed up when he destroyed his 3-wood after a poor approach shot at the 16th. I feel like I can get to tucked pins by carving it a little bit more left to right or right to left into some of these pins, and the bounces will reward those shots.
Stenson capped off his victory in style, pumping a 310-yard 3-wood down the 18th fairway - almost hitting it too well as it came up a foot shy of a bunker - and then finding the center of the green to take away any nerves from his putt, which he buried anyways to make his round a record-setting one.
Stenson only cared about that silver claret jug.