HILTON HEAD ISLAND, S.C. (AP) - Carl Pettersson had a run of five straight birdies on the front nine and finished with a birdie on the 18th hole for a 66 and a one-stroke lead over Colt Knost after the third round of the RBC Heritage on Saturday.
Pettersson held a three-stroke lead through 10 holes, yet was tied with Knost after the 15th. Pettersson moved in front with the round's final putt, an 8-foot birdie on Harbour Town Golf Links signature closing hole.
Knost's roller coaster of a round included an eagle on No. 2 and several missed fairways on the tight holes of Harbour Town Golf Links. Still, he kept close enough with a 69. He'll be paired with Pettersson again Sunday in the chase for his first PGA Tour win.
Zach Johnson, the 2007 Masters winner, shot a 66 to move to third at 8 under, three behind the leaders. Two-time RBC Heritage champion Boo Weekley had a 70 and was in fourth another shot behind. Defending champ Brandt Snedeker (69), Kevin Na (70) and Robert Garrigus (70) were next at 6 under.
World No. 1 Luke Donald failed to make a move toward keeping the top spot, his even-par 71 leaving him at 2 over and tied for 52nd. Donald needs to finish eighth or better to fend off No. 2 Rory McIlroy, who like Masters champion Bubba Watson and most other top golfers, was taking the week off.
Pettersson threatened to turn the tournament into a runaway with his early birdie streak. Knost would not let that happen, overcoming some unsteady play to keep close to his playing partner.
It sure wasn't easy for Knost.
He came to the first tee with a two-stroke lead, then knocked his opening tee shot into some pine straw right of the fairway and took bogey. He followed that by rolling in a 48-foot eagle putt from the left fringe on No. 2 and flashed a wide smile that even had Pettersson grinning.
Knost's up-and-down ride continued through the front nine. There was the lipout on No. 3 for bogey, the layup and chip to 10 feet on the par-5 fifth for birdie, and solid par saves from the bunker on No. 7 and from some more pine straw on No. 8.
Then on the ninth after another wayward drive, Knost punched it to 10 feet and made the birdie to stay one behind Pettersson.
Things swung Pettersson's way once more on the 10th, his lead growing to three shots after he made birdie and Knost was short on his approach and missed an 8-foot attempt at par.
Still, Knost kept grinding. A birdie on the 13th hole drew Knost with a stroke and the pair was tied at the top at 11 under when Pettersson took bogey on the par-5 15th hole.
The two matched pars until the windswept 18th when Pettersson struck a stunning approach that slid by the cup and settled 8 feet past. He rolled in the putt with a smile on his face.
Johnson put together his second straight sub-70 round to move into third. He has largely struggled at Harbour Town, his best showing a tie for sixth the week after he slipped on the green jacket five years ago. Johnson's round took flight with an eagle on No. 5. He closed with birdies on the 16th and 18th as he looks for his first victory since the Crown Plaza Invitational at Colonial in 2010.
``We've still got 18 holes,'' Johnson said. ``The last four or five holes, if I'm near the lead, we can get after it a little bit.''
Donald, starting almost five hours before the leaders, never got things going. Without an absolute miracle he will fall from No. 1 after he finishes Sunday, surrendering the top spot to McIlroy, who is off spending time with girlfriend Caroline Wozniacki as she competes in Denmark, according to the tennis star's tweets. Donald took the top spot from McIlroy last month.