Lee Westwood shot a course record 62 to earn a seven-shot lead after the third round of the Nedbank Golf Challenge at the Sun City resort in South Africa.
The world number three carded 10 birdies and no bogeys to move ahead of overnight leader Graeme McDowell, who shot a two-under-par 70.
The Northern Irishman shares second spot with Sweden's Robert Karlsson on nine under.
Jason Dufner and Martin Kaymer are a further shot behind.
Birdies came in bursts for Westwood - first between two and four, another run of three between nine and 11 and most spectacularly of all a streak of four between the 14th and 17th, completed when he stroked in a six-foot put to ease to 10 under.
Westwood found the edge of the green with his approach to the 18th as he chased a fifth birdie in a row, but left his putt just short.
"I obviously played pretty well," said Westwood. "I can't remember missing a fairway, and I played the par-fives really well - I had four really good eagle chances on them and didn't make any of the eagle putts.
"It's the way I've been playing tee-to-green. I've just been waiting for one or two 20-footers to go in, and I felt like I had a 62 in me."
McDowell trailed by five going to the 18th but made a mess of the final hole, making a double-bogey putt after twice going into the bunkers.
Home favourite Charl Schwartzel recorded the second best round of the day with a four-under 68 which left him in a share of sixth with Kim Kyung-tae.