The South African, who won last week’s Joburg Open, had nine birdies – eight of them on the first 12 holes – to lead Padraig Harrington (65) by one.
U.S. Open champion Graeme McDowell (66) survived a ruling scare on the final hole and finished with five straight birdies, sharing third place with Swedish pair Alexander Noren and Niclas Fasth.
The 26-year-old Schwartzel, who finished inside the top four in the four opening tournaments in South Africa, bogeyed the par-4 17th but then birdied the 18th.
Despite his leading score, Schwartzel said he’s been struggling with his swing.
“I have been hooking the ball. In my entire career, I’ve never hooked the ball,” Schwartzel said. “Playing some of the courses in South Africa, if you miss the fairway, there’s no rough. Last week was a golf course that I played lots of golf on and felt comfortable with it. I played well for the first 63 holes. The last nine holes were a real struggle.”
Defending champion Martin Kaymer (67) was close behind the leaders, tied with Danny Willett at 5 under. Lee Westwood (69) and Masters champion Phil Mickelson (71) are also near the top.
“I hit the ball very well and kept the ball in play off the tee and hit a lot of good iron shots. I didn’t make very many putts,” Mickelson said. “I’ve been able to work here with Butch Harmon and this is a good foundation week. We have put in some good work and my golf game feels much sharper than the score indicated.”