Colt Knost fired a five-under 66 on Friday to take a two-stroke lead after two rounds of the Heritage.

Knost held a share of first place after the opening round, but is alone at the top of the leaderboard at nine-under-par 133. Carl Pettersson carded a 65 to move up to second place at minus-seven. Both had the benefit of playing in the morning wave, when wind was minimal.

The 26-year-old Knost had a very successful amateur career and won twice on the Nationwide Tour, but is still in search of his first PGA Tour victory.

He has had an up-and-down season so far in 2012. Knost tied for third at the Mayakoba Golf Classic in February, but has also missed the cut or finished above par six times in eight events.

However, Knost said he feels like he's starting to get his game back to where he likes it.

"I had one good finish this year, but I'm making a lot of cuts, which is a step in the right direction for me," Knost said. "Today I felt so comfortable out there being around the lead, even though it's only Friday. I think I'm going to feel great this weekend."

He is in good position, with only five players within four strokes. Two-time champion Boo Weekley (66) and Harris English (68) are tied for third at six-under, while first-round co-leader Chad Campbell (70) and Robert Garrigus (66) are another shot back in fifth.

World No. 1 Luke Donald shot a two-under 69 to save his tournament with his ranking on the line. He needs to finish within the top eight to retain the top spot, and needed his Friday round to make the cut.

Still, he sits at two-over par in a tie for 56th, and getting to the top of the leaderboard will take some low scores during the weekend at Harbour Town Golf Links. If he doesn't get within the top eight, Rory McIlroy will ascend to No. 1 despite not playing this week.

Knost's round got into red numbers at the 13th, his fourth hole, where he rolled in a six-footer for birdie. He then mastered the tricky par-three 17th, which on Friday had the pin in the narrow part of the green, above a large bunker and below a smaller one.

But he managed to stick his tee shot eight feet from the hole, then drained the putt to reach minus-six.

Once around the turn, Knost maintained his momentum. He rolled in a 24-footer for birdie at the first, then came back with another at the second. Knost's second shot at the par-five landed in a bunker to the right of the green, but he blasted out to five feet and sank the putt.

Three holes later, he found himself in a similar predicament -- this time in a left greenside bunker. But Knost once again blasted out close to the pin, knocking in a three-footer for birdie.

Pettersson rose up the leaderboard thanks to a remarkably accurate round. He made seven birdies, and almost all of them were the result of a great approach or good short game.

He started rising up the leaderboard thanks to a quick start, which included a near-eagle at the par-five second. He chipped his third within 10 inches and made the easy putt for birdie.

The Swede then birdied his next two holes with putts of four and six feet, getting to minus-four in the process.

Pettersson stayed at that score around the turn, then sank back-to-back birdies early on his back nine. Another accurate approach shot set up a one- footer at the 11th, and he guided in a 13-footer at the 12th.

The 34-year-old stumbled to a bogey at the 15th, but made up for the mistake by ending his round with consecutive birdie putts of three feet.

"I've been driving the ball good for a couple of years and my iron game hasn't been as sharp," Pettersson said. "But the last few weeks my irons have been really good. And I'm putting pretty good. I finished up with two great iron shots today."

Defending champion Brandt Snedeker shot a 67 to move to four-under, and shares seventh with four others, including Bob Estes, who aced the par-three fourth hole on his way to a 67. Fredrik Jacobson (67), Michael Bradley (64) and Kevin Na (68) also sit at minus-four.

NOTES: Vaughn Taylor, the third of the first round co-leaders, carded a 73 to fall into a tie for 16th at minus-two...Bradley's 64 is the best round of the tournament so far...The 36-hole cut fell at three-over 145, and those to miss it include Padraig Harrington, Ernie Els and Rickie Fowler.