Jim Furyk bogeyed the 18th to surrender his outright lead heading into the final round of the Verizon Heritage after facing some real competition from playing partner Aaron Baddeley.
The American found sand behind the green and only just escaped from the trap, resulting in a bogey five which dropped him back to 14 under par alongside Baddeley.
And with Ernie Els four shots back in fourth, the pressure is likely to increase on the top two tomorrow.
Australian Baddeley, who finished yesterday with an eagle two after holing his 160-yard approach to the 18th, had three birdies in his first five holes to move to 12 under despite the breezy conditions at the Harbour Town Links.
Furyk, who led by two overnight, initially responded to the challenge with birdies at the first and fifth but he dropped shots at the seventh and eighth to concede the lead.
But when Baddeley found the greenside bunker at the 11th and could not get up and down he fell back to 11 under with Furyk.
Both then birdied the next, Baddeley from 18 feet and Furyk from nine feet, with the former edging ahead again by picking up a shot at the 13th
At the par-five 15th Furyk birdied from eight feet while his partner missed from six and they were level again at 13 under.
The American then hit his 132-yard approach to two feet for a birdie at the next, with Baddeley holing a 10-footer to match him, but Furyk’s renowned iron play lifted him to 15 under at the short 17th with a tee shot to 12 feet.
However, he over-shot the last green and paid the penalty to finish with a 68 to his partner’s 66.
Billy Mayfair produced two birdies in his last four holes for a round of 68 to go third on his own at 11 under while world number five Els carded a six-under-par 65, level with American Jerry Kelly.
Four birdies in his first five holes allowed the South African to quickly advance from his overnight four under.
A bogey four at the seventh was followed by a double-bogey six at the next but Els pulled one back at the ninth to turn in 34 and then another at the 11th before three back-to-back birdies from the 15th saw him finish as strong as he started.
“It was a fun day today. I have been trying to get myself going over the last couple of weeks and when you put a lot of work in and don’t get the run you normally start questioning yourself and I didn’t want to do that. Today was a nice day,” said Els.
“Before today I hadn’t made many putts. Right now it feels like I don’t have too many weaknesses.
“The wind is really playing some games out there. The 16th and 17th are the toughest holes today.
“Coming down the stretch you have opportunities for birdies but you have to be careful.”
England’s Ian Poulter dropped back to two under after a one-over-par round of 72, having started with two birdies in his opening six holes, while compatriots Brian Davis (75), Justin Rose (74) and Greg Owen (74) saw their hopes of mounting a challenge disappear.