Seven players are tied for third at 4-under while defending champion Tiger Woods, using a new driver, settled for a 70.
Roberts, who turned 49 a week ago, is known for his putting prowess. He said, however, he took his first putting lesson ever on Wednesday.
"I actually had someone take a look at me and we made a slight adjustment, and it really paid off," Roberts said.
Ben Curtis, who used his 13th place finish here last year to qualify for the British Open, which he went on to win, was among those tied for third.