Phil Mickelson instantly turned the tables on Henrik Stenson as what was expected to be a private duel between the pair for the Open Championship got under way.
Stenson took a one-shot lead into the final round at Royal Troon, only to three-putt the opening hole from just short of the green after Mickelson had already fired his approach to within two feet.
The resulting birdie took Mickelson to the top of the leaderboard in pursuit of a second Open title and the same result from Muirfield in 2013, where Stenson finished runner-up.
The 46-year-old, who has not won a tournament since lifting the Claret Jug three years ago, would be the fourth oldest winner of any major and the oldest in the Open since 1867, while 40-year-old Stenson was looking to become Sweden's first male major champion.
Improving conditions gave the chasing pack more hope of mounting a challenge to the final pair, although Bill Haas remained six off the lead after two opening pars.
England's Andrew Johnston was a shot further back after following a birdie on the first with a bogey on the second, with 2014 champion Rory McIlroy on four under par after racing to the turn in 32.