Jason Dufner had two eagles in a six-under par 65 on Saturday to take a one-shot lead going into the final round of the US PGA Tour's Heritage in Hilton Head, South Carolina.
Dufner eagled both par-fives on the front nine, rolling in an 11-footer at the second and pitching in from off the green at the fifth hole at Harbour Town.
His 13-under par total of 200 put him one in front of Canada's Graham DeLaet, who lost a share of the lead with a bogey at 18 to cap a 69 for 201.
Dufner also had three bogeys on the front nine, but in addition to his eagles he had five birdies on the day, four of them on a solid back nine.
"The front nine was a little bit of a rollercoaster," Dufner said. "It's always nice to get an eagle, let alone two.
"The back nine was really clean. I was really happy how I played on the back nine."
Overnight co-leader DeLaet opened his round with a bogey, then had four birdies before stumbling again at the last.
He was one stroke in front of Americans Kevin Kisner, who carded a 66, and Webb Simpson, who signed for a 68.
"It was disappointing to finish with a bogey on the last hole, but obviously I've been playing well and I'm excited about (Sunday)," said DeLaet, who has won three times on the PGA Tour Canada but has never won in 159 prior PGA Tour starts.
"I'm looking forward to the challenge of playing with Jason. I've played with him a few times before and it should be fun."
England's Ian Poulter was alone on 203 after a 69. Poulter had powered to the lead with four birdies on the front nine before opening the back nine with a double bogey and a bogey.
Poulter, playing on a major medical exemption, has this week and one more start to collect the prize money he needs to secure his playing status for the rest of the season.
Since returning from a foot injury in October Poulter has made eight starts on the US tour, making five cuts.
England's Luke Donald, who shared the 36-hole lead, had two bogeys and a birdie in a one-over 72 that saw him drop four shots off the pace.
He was joined on 204 by Americans Wesley Bryan and William McGirt, who both shot 68.