The South African carded seven birdies - the highlight a lengthy putt at the 11th - to put himself in the frame for a second WGC title of the season.
"I putted nicely today," said Els. "I think somebody said I had 25 putts, and that's kind of what you need to score well.
"I felt I was in control of my ball off the tees and I gave myself a lot of opportunities. When I didn't, I got the ball up and down - it was a really nice round."
On a congested leaderboard, Americans Ryan Palmer and Sean O'Hair were leading the way on eight under with two and three holes to play respectively.
Four players were alongside Els on seven under out on the course - the American trio of Matt Kuchar, Justin Leonard and Lucas Glover joined by England's Oliver Wilson.
The Ryder Cup star is still seeking his first European Tour title, but added to an outward 31 with a birdie at the 14th to be five under for the day with three to play.