The Thai has twice been a runner up in Rolex Series events but after missing 11 of his first 15 cuts worldwide in 2021 following an injury disrupted 2019 and Covid interrupted 2020, he would not have been among the favourites arriving at Wentworth Golf Club.
But the 32-year-old is not a four time European Tour winner for nothing and he followed up his opening 64 to get to 12 under and lead by one shot from home favourite Laurie Canter, who carded a 66, and Italian Francesco Laporta who signed for a bogey free 65.
In the race for Ryder Cup places, Ireland's Shane Lowry was in the group a further shot back, while Austrian Bernd Wiesberger enters the weekend six shots off the lead knowing a top 50 could see him make the team.
Aphibarnrat birdied three of his last four holes to catapult himself up the leaderboard but was not getting carried away at an event where he finished fifth in 2018.
"I'm really proud of the way I'm playing these first two rounds," he said. "A lot of good stuff in there.
"Everyone tried to get a low score but this golf course, you can hit a lot of birdies but it can hurt you if you're out of position. I tried to play for more fairways, more greens. My putter was rolling well this week and I'm really pleased.
"I don't want to really set a goal, to be honest. I just want to go out there and swing, what I'm doing the first two rounds, do the same thing I'm doing, try to hit fairways, greens. Whatever the result, at the end of the day, I just accept it."
A two putt birdie on the fourth was followed by an approach to five feet at the seventh as Aphibarnrat got within one of early starter Canter at the turn.
A birdie on the 12th was sandwiched by a pair of bogeys but he almost made a hole-in-one on the 14th before joining the lead from 14 feet on the 16th and getting up and down on the next.
Canter produced wonderful iron shots on the third, fifth and ninth and made a two putt birdie on the fourth to turn in 31 before finding the water on the 12th for a first bogey of the day.
More dialled in iron play brought gains on the 13th and 15th and, while he failed to get up and down on the next, the 31-year-old made the most of the two closing par fives.
Laporta put an approach to eight feet on the third and followed it with a two putt birdie on the fourth before holing a long putt on the sixth.
He holed another impressive putt on the 15th to go with approaches inside five feet on the 13th and 16th before being forced to lay up and draining a 20 footer in the fading light on the last for another birdie.
Scott had a roller coaster start, hitting straight back from an opening bogey but making a double on the third before eagling the fourth after putting his second to 11 feet.
A bogey on the ninth saw him turn over par but he made a hat-trick of gains from the 11th, dropped a shot on 14th, and finished birdie birdie to get to double figures with a 69.
Horschel - who would move to second in the Race to Dubai Rankings in Partnership with Rolex with a win - birdied five of his last six holes in a bogey free 65, one shot better than Donaldson, who made three eagles in his round.
A win could see Rose book his place at the Ryder Cup and the Englishman made six birdies and two bogeys in a 68.