Luke Donald's quest to regain the world number one spot was boosted by a seven-under-par second round at the Classic of New Orleans.
The 34-year-old needs to finish in the top seven to move back to the top ranking, and that looked unlikely after a one-over-par 73 on Thursday left him eight adrift of the leaders.
However, he stormed back into contention, kicking off with a birdie at his opening hole - the 10th - before adding four further birdies and an eagle two at the par-four first to claim a share of 12th place.
Scotland's Russell Knox was 11 under overall, one shot behind clubhouse leader Jason Dufner with a shot to play.
Australian Greg Chalmers and South African Ernie Els were in a tie for third at 10 under after a 64 and a 66 respectively. Joint first-round leader Ken Duke was one under par through seven holes, while fellow opening-round leader Cameron Tringale made a bad start as he bogeyed the 10th, his first hole.
Masters champion Bubba Watson was down in a tie for 66th, even par for the day through five holes and one under overall.
