Roberts, the first-round leader by one, finished 36 holes at 9-under 133 to take a two-shot lead into Sunday's final round.
At various points during the front nine Saturday as many as nine golfers shared the lead. Roberts got sole possession of the lead at the 15th when he sank a six-foot birdie putt to go to 8-under.
Roberts, who placed second last year, has three runner-up finishes in 2008, but no wins. His last victory came at the 2007 Senior Players Championship.
Last week, he held the 36-hole lead at the Bank of America Championship.
Denis Watson (67), Fulton Allem (67), Mike Goodes (68), Mark McNulty (69), Gene Jones (70) and defending champion Lonnie Nielsen (69) are tied for fourth at 6-under 136.