(CNN) -- Brian Gay strengthened his grip on the Heritage in South Carolina as Briton Luke Donald made his move onto the leaderboard at Harbour Town Golf Links.
Brian Gay is hoping to claim his second victory on the US PGA Tour following last year's triumph in Mexico.
Ryder Cup player Donald set the leaders a target after shooting a third-round, six-under-par 65 having spent the second round making sure he would make the cut.
American Gay responded despite toughening wind conditions and increased his advantage to three shots over the field with a third-round 67 that took him to 13 under par.
He will start the final round confident he can post another low score and register his second win on the US PGA Tour following a maiden victory at last year's Mayakoba Golf Classic in Cancun, Mexico.
"Another good day," Gay said. "I continued to drive it well and hit the ball well. "I think if I can go out and continue to do the same things, I'll be in pretty good shape.
"Anybody can go low at any time, but I feel like the way I'm swinging and playing, I can go out there and shoot another score."
Australia's Tim Wilkinson matched Donald's 65 to move into second place on 10 under while Lee Janzen improved by two strokes with a 69 to take third at nine under.
Former Open champion Todd Hamilton, who began the day a shot behind Gay on eight under, shot a level 71 and fell to fourth place heading into the final round.
Donald, who is one of three players tied for 10th place, opened the tournament on Hilton Head Island with a two-over 73 and carded a 70 on Friday to progress to the weekend at one over par, two strokes inside the cut line.
There was a big improvement on Saturday, though, as Donald, taking advantage of calm conditions on the Atlantic coast, opened with a birdie and then bounced back from a bogey at the par-four third to hole six more birdies and move to five under for the tournament.
Germany's Alex Cejka is one shot better and remains the leading European, but had a 72 to add to his opening 64 and second round 71.
Ernie Els took a six at the par-four ninth and a seven at the par-five 15th on the way to a 73, while Paul Casey finished on a high note with an eagle three at the 15th to help him to a 69 and take the Englishman to one under with the South African.
Northern Ireland's Rory McIlroy continued to find Harbour Town a struggle. He shot a one-over 72 to finish as two over for the week and yet to break par.