Roberts held a three-shot lead on Funk at 10-under 200. Roberts will be seeking his third Champions Tour major on Sunday.
Funk, who has never won a major on any tour, hit every fairway and missed just two greens in regulation during the third round, finishing at 7-under 203. He had the best round of the day Saturday, a 4-under 66.
"It was the best ball-striking round I've had in a long while," said Funk, who has won on both the Champions Tour and the PGA Tour this season.
Tom Watson turned in a 68 and was in third place at 205. The reigning Senior British Open winner made a bogey from the rough at the 18th to fall five shots off the lead.