His home fans delighted since he chased an introduction 64 to assert the first-round lead.
An carded eight birdies in his own blemish-free round to make a one-shot guide over rising star Joakim Niemann, while world # 1 Brooks Koepka birdied the 16th and then eagled the last to salvage a 69.
Four birdies within the first seven holes obtained An off the beginning he needed and, the home preferred reeled off three consecutive birdies from the 11th and added a second at 16 for to eight under, later turning in 32.
The BMW PGA champion was not able to make the most of this last, but he had done enough to become installed as leader and also An was delighted – and somewhat surprised – along with his start at Jeju Island.
It was fantastic, eight under and bogey free is always great, he explained. I hit it really solid, and that I wasnt anticipating it, to be honest. I didnt hit it on the range today and that the last couple days, but what seems to be running.
Everything was moving in the flag the perfect distance and I holed a great deal of putts today, so everything just clicked and I took bogey free.
I can feel a lot of support from people here. And playing nicely before them is a bonus. Hopefully, I can keep this going.
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Niemann was only two under at the turn, however, the young Chilean started the back nine made two more at 18 and 17 to complete a 65 without a bogey.
Day has shrunk to 27th at the world rankings and is Australian supporting Adam Scott and Marc Leishman having not played since the BMW Championship in August, but he gave himself a lift using a 66 which included four birdies around the turn.
His compatriot Cameron Smith is among a set of five players under, although 2017 winner Justin Thomas carded six birdies but blotted his card bogeys at the 18th and second holes to slip .
Graeme McDowell finished both nines with a pair of birdies because he also kept the errors at bay in a solid 68, also Ian Poulter was going well at four under two to play in front of a bogey at the short 17th watched him slide into a tie for 15th with Tyrrell Hatton, Viktor Hovland and Koepka.
The world No 1, that missed the cut in Las Vegas two months ago, had been erratic within the next half of his round while Tommy Fleetwood also fought for consistency and also mixed three birdies with two bogeys in his 71.
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