Former U.S. Open champion Graeme under 67 on Friday to take the second-round lead of the Nedbank Golf Challenge.
McDowell finished 36 holes at the Gary Player Country Club at seven-under 137 and is one shot clear of several players in this limited-field, lucrative event in Sun City.
Simon Dyson and Kyung-tae Kim both carded rounds of two-under 70 on Friday and share sixth at four-under 140.
They're all chasing the man from Northern Ireland who won last year's U.S. Open at Pebble Beach.
McDowell birdied the first hole, then parred his next seven holes. After a fortunate par at No. 8, McDowell caught fire around the turn to vault atop the leaderboard.
At the par-five ninth, McDowell's second barely cleared water and he got up and down from the fringe for birdie. He birdied the par-five 10th and made it three in a row with a birdie at 11.
McDowell chipped in for yet another birdie at 13 and was one stroke clear of the field.
Trouble loomed on the par-five 14th. McDowell knocked his drive into the bushes and took two strokes just to get it back to the fairway. He hit his fourth from the short grass into a greenside bunker, blasted out, then took two putts for a double-bogey.
"The second shot can only be described as an air shot, really," admitted McDowell. "My ball was sitting on a rock, and I contacted it about an inch behind the ball, hit the rock and my club just bounced right over the top of the ball."
McDowell fell out of the lead after the disaster at 14, then re-joined the mix at the top with a 20-foot birdie putt at the par-three 16th. He moved clear of everyone with another 20-footer for birdie, this time at the closing hole, to grab sole possession of first.
"There is so much trouble lurking on this golf course," said McDowell. "You've got to be really decisive off the tee. The second you start steering, you get into big trouble."
NOTES: First-round co-leader and reigning Masters champion Charl Schwartzel struggled to a two-over 74 on Friday and fell into 10th at minus-two...Open champion Darren Clarke is 11th at one-under par, followed by Francesco Molinari, whose five-over 77 left him at the bottom of the leaderboard at plus-five.