Cink, the 1997 winner at TPC River Highlands, is seeking his first victory of the season after six top-10 finishes.
"I hope it's just a matter of time," Cink said. "I hope it's a matter of about two days."
It didn't look good early for Cink, who began the day at 4 under and promptly bogeyed the first two holes. He got one back with a birdie at the third before knocking in a 26-foot putt for eagle on the par-5 sixth. He bettered that shot by curling in a 49-foot right-to-left eagle putt on the 13th.
"I just kept staying down and staying focused on doing what I can do and that's just stroking the putter through the ball, almost not looking up to watch it," said Cink, who opened with a 66 on Thursday en route to a 10-under 130 total.
Mahan shot a 63, the best round of the day, to join Ken Duke and Lucas Glover at 9-under. Duke and Glover shot 66s.
Mahan has been under par in 10 of his last 11 rounds at the TPC River Highlands, where he won last year in a playoff with journeyman Jay Williamson. Mahan tied for second in 2006, and has made five consecutive cuts on the course.
"I just feel comfortable here," Mahan said. "I make a lot of free swings and I can play golf and I don't have to worry about where the ball might end up."
On Friday, the ball usually ended up in the fairway, on the green or in the hole. The 26-year-old Mahan shot a bogey-free round, with seven birdies, including four on his first seven holes. He hit all 14 of fairways and 15 of 18 greens.
Mahan would be only the second back-to-back winner in the 55-year history of the tournament. Phil Mickelson won in 2001 and 2002.
Duke and Glover followed first-round 65s with their 66s.
"It was a good day, I mean a steady day," Duke said.
Ninety-eight players finished the first two rounds under par, and 72 made the cut at 3 under, the lowest cut on tour this season.
