With the leading pairs still to tee off on a pleasant day on the Antrim coast, An made headway as he got himself to five under, just three off the lead held jointly by Ireland's Shane Lowry and American J.B. Holmes.
An, who carded a four-under 67 on Friday, gathered birdies at the second, fourth, fifth and eighth to jump 20 places up the leaderboard into a share of fifth before a bogey at the ninth undid some of his good work.
|Park Sang-hyun (Yonhap)|
Fellow Korean Park Sang-hyun was also shifting on the day dubbed "moving day" at majors, reaching five under for the tournament after 12 holes on the Dunluce layout which was offering plenty of good scoring opportunities.
American Xander Schauffele, who challenged strongly at Carnoustie last year, was also putting himself in the mix as he picked up three strokes after eight holes to move to six under.England's Danny Willett was on four under for his round after 11 holes and five under for the tournament. (Reuters)