Adam Scott took full advantage of relatively benign conditions on the Ayrshire coast for early starters to resurrect a title challenge he thought was long gone.
But Jason Day saw his hopes all but disappear in the afternoon wind and rain.
Scott started at five over par, 12 shots behind overnight leader Shane Lowry, but birdied the first two holes as he set the tone for a four-under 32 to surge 41 places by the turn.
The back nine was a stiffer test, but he finished with a five-under-par 66 to head the early finishers with an even score after 54 holes.
Scott's fellow Australian, former world No.1 Day, was one under when he started five hours later, but within two holes he was already over par having bogeyed both.
It did not get much better and after a dispiriting round in miserable conditions he ended four over after shooting 76.
Scott's 66 was good enough for a solo clubhouse lead for 90 minutes before Justin Thomas joined him after recording a four-under round. Half-an-hour later Thriston Lawrence went past them both after a round that began in electrifying fashion with six birdies in the first eight holes.
Thereafter, however, not many went past and Scott ended the day one of three players tied for tenth. Day, however, is one of seven players tied for 33rd, eight shots off a lead held by Billy Horschel on four under.
"I think I got what I deserved out there," said Scott. "I played some fairly good golf and didn't make too many errors."
Speaking before the conditions played havoc with the overnight leaders he added: "I'm probably not going to be in the mix, let's be honest. I'm likely nine shots behind, seven to nine shots behind, I would guess.
"If I am, then that's a bonus, but I'm going to need wind and everything to be in my favour to kind of be in the mix."
While Day bogeyed the first two holes, Scott birdied both, nailing puts from 14 and 17 feet.
He then scrambled well to par the fourth after landing in a fairway bunker and having to chip out sideways.
A superb tee shot to within five feet at the par-3 fifth delivered a second birdie and the 44-year-old took advantage of a free drop at the seventh to land another, via an 18-foot putt.
Another fine tee shot brought a successful 11-foot birdie two at the 14th while the South Australian also birdied the undemanding 16th. Unfortunately sandwiched in between he dropped a shot at the 15th missing a par putt from less than four feet, the only putt he missed from less than 10 feet during the round.
Scott headed inside with impeccable timing as the rain arrived and the wind picked up.
Day, however, was just beginning. After his chastening start the Queenslander fought back with a birdie on the fourth despite finding a greenside bunker with his approach.
A 26ft putt at the eighth brought him back to level par for the round and he went to the turn still in contention. However, he then missed putts inside ten feet, five feet and four feet to bogey the 10th, 13th and 14th. At the 15th a poor approach cost him another shot and at the par-3 17th he drove well wide of the green.
Day's only hope appears to be for a repeat on Sunday of Saturday's weather pattern, but the forecast suggests he will be frustrated.
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