Clarke, who said he made some key adjustments to his swing last week at the Masters, was at 12-under par 130 midway through the tournament.
Lonard, who narrowly missed equaling the course record in the opening round, had to settle for a 3-over 74 Friday.
"Sunday at Augusta, I worked on a couple of things and felt very comfortable there and hit the ball very well on the last day," Clarke said.
"Actually I wasn't releasing the club enough, and I worked on it there and I worked on it here. So far, so good.
"I'll just keep doing what I'm doing and try to make as many birdies as I can."
Five-time champion Davis Love III was at 139.