A superb run of five birdies in a row helped Carl Pettersson into the lead after three rounds of the RBC Heritage, while Luke Donald looks set to lose his World No 1 ranking.

Pettersson’s 12-under total was good enough for a one shot lead over American Colt Knost in the $5.7 million Heritage event.

"It was tough," Pettersson said. "The wind died down and got back up. The greens were quick. I played a really good round. I'm happy. I was able to finish strong."

"I have to play my game and stay calm," the Swede said. "I feel like if I play well I have a good chance."

There are a lot of good players lurking not far off the lead including Zach Johnson in third, Boo Weekley in fourth and Kevin Na, Robert Garrigus and Brendt Snedeker all tied for fifth.

England’s Donald needs to finish in the top seven to keep his rank as the best player in the world, but will start the final day well off the place in a share of 52nd on 2-over par.

"Now that I've been No 1 for a number of weeks now, it's not something I think about too much," Donald said.

Knost sandwiched an eagle between two bogeys to remain hot on Pettersson’s heels.

"I got off to a little bit of a rough start. The putter saved me," Knost said. "It wasn't a great day but I'm looking forward to tomorrow. It wasn't my best but I feel like I can be ready for tomorrow."