South African Ernie Els birdied three of the last six holes to sign for a third-round 68 to sit just three shots behind Jason Dufner at the top of the leaderboard.

American Dufner is closing in on a maiden PGA Tour title after an impressive 5-under 67 in the third round.

"A pretty nice round again," the laid-back 35-year-old told reporters. "I got off to a really nice start there with three birdies in the first five holes, and that's kind of nice on this course.

"I was pretty solid, never was really in too much trouble. I hit a lot of fairways, a lot of balls in play and lot of greens or just off the greens."

Dufner, who twice lost out in playoffs on the PGA Tour last season, mixed four birdies with a lone bogey to reach the turn in three-under 33.

"Right now a win would be great," said the American, who has been a runner-up three times on the PGA Tour. "I've been knocking on the door with a lot of solid rounds, a lot of solid play last year at the end of the year."

Asked whether he would be able to control his emotions in Sunday's final round, Dufner replied: "I think I do a pretty good job with that.

"Obviously you're going to have some thoughts about winning tournaments when you're in a position like this, what your expectations might be, how you're going to respond tomorrow when you step on that first tee.

"The toughest part for me is that warm-up session and leading into maybe the first hole or the first tee shot. But for me, usually when the day is over, I'm done with it."

British world No 2 Luke Donald struggled in the first round but was delighted to finish the third day five shots off the lead having 65 in the second round and with a seven-birdie 66 in the third.

"It was just a solid round," the Englishman said. "I had kind of a slow start on Thursday but 13 under for the last 36 holes is very pleasing and I'm playing a lot better. I'm back here in the mix a little bit."

Masters champion Bubba Watson initially struggled with fatigue this week, but regained form with a 65 on Saturday to end the day eight shots off the pace.