Im Sung-jae shot a second-round six-under-par 64 to hold a share of the lead at the halfway stage of the Honda Classic at Palm Beach Gardens.
The South Korean followed up his opening 70 with a round with featured seven birdies and one bogey to head the leaderboard alongside American Keith Mitchell, who went round in 66.
Another American Lucas Glover was a shot further back after a 69, ahead of a group of nine players on four under, including three-time major champion Brooks Koepka, who also carded a 69.
Overnight leader Jhonattan Vegas could only manager a 73, making two double bogeys, as he slipped back to three under, alongside Sergio Garcia.
Graeme McDowell recovered from three successive bogeys early in his round to finish with a level-par 70 and two over overall, which was enough to take him into the weekend.
The Antrim man birdied the 16th and 17th holes to make the cut with a shot to spare.
Seamus Power slumped to a 78 that included two double bogeys and exited the tournament on 11 over.
The likes of 2012 winner Rory McIlroy and Tiger Woods are among the star names who have opted to skip the $6.8m Florida event.