Kyle Stanley took a one-stroke lead and Rory Sabbatini equalled the course record on an eventful second day at the Honda Classic in Florida.
Stanley, who was one shot off the pace following Thursday’s wind-affected opening round, fired a four-under 66 to lead the field on six-under overall at the halfway point.
But it was South African Sabbatini who was the toast of the round after equalling the tournament’s course record with a remarkable six-under 64 at the PGA National Champion Course in Palm Beach Gardens.
Sabbatini’s record-equalling round pulled him to within one stroke of Stanley, with compatriot Charl Schwartzel two shots back in outright third after firing a second round of 69, and a group of four, including Australian Stuart Appleby, a further shot back at two under the card.
World number two Lee Westwood, who can reclaim his number one ranking from Martin Kaymer with a solo third place finish or better, carded three late bogeys to slump five shots adrift of Stanley.
Stanley began on the back nine and rocketed up the leaderboard with a hat-trick of birdies from the 13th hole.
He moved to four under and an outright lead with another birdie at the first, but was forced to take a five at the par-four second, ending his bogey-free streak of 26 holes.
The American fired off another two birdies at the fourth and fifth to move two strokes clear of the pack, before another bogey at the sixth dropped him back to six under.
Sabbatini, meanwhile, birdied five of his final 10 holes to become just the sixth pro to shoot 64 since the Honda moved to PGA National four years ago.
The South African joins Luke Donald, Justin Rose, Anthony Kim, Stephen Ames and Mike Weir as golfers who have recorded the achievement.
Westwood started promisingly and was four under for the round after back-to-back birdies at the 11th and 12th holes.
But it all fell apart soon after, the Englishman bogeying three of his last six to drop from outright third all the way back into a five-way tie for eighth.
He is joined on one under by Matt Kuchar (70), Gary Woodland (68), Yang Young-eun (71) and overnight leader Spencer Levin (72).