Roberts finished with a tough up-and-down par from below the 18th green at Baltimore Country Club and held a three-shot lead on Funk at 10-under 200.
'I hit a really good spot in the middle of the round. But my putter saved me on the last few holes,' said Roberts, who 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 that kept Roberts on his toes.
'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 shot a 2-under 68 and was alone in third place at 5-under 205. The reigning Senior British Open winner made a sloppy bogey from the rough at the 18th to fall five shots off the lead, leaving Roberts and Funk in good position to go head-to-head for the win Sunday.
Mark Wiebe (69), Des Smyth (70) and David Eger (70) were tied for fourth place at 4-under 206, six shots off the pace and all but out of contention. Jay Haas, Dana Quigley and Gil Morgan were the only other players within seven shots of Roberts.
The man they call the 'Boss of the Moss' will not only be seeking his third Champions Tour major on Sunday, he will also be looking to reverse a recent trend that has hijacked opportunities for further majors.
Roberts hasn't broken par in the final round in any of the last nine over-50 majors.
At this event last year, he coughed up a two-shot lead in the final round when he shot a 74 on Sunday at the TPC of Michigan. His lead was as big as five shots before a nasty stretch run that included two double-bogeys and a bogey.
Bobby Wadkins ended up winning despite making a double-bogey on the 18th hole.
'I really let that one get away last year,' said Roberts. 'But I've forgotten about that and I'm just going to go out and keep doing what I've been doing. I felt like I've hit some good shots and I'm just going to focus on that tomorrow.'
The week before last year's Senior Players, Roberts lost a final-round lead at the U.S. Senior Open after setting a USGA scoring record the day before when he scorched Prairie Dunes for a 62.
'I feel like I'm getting a little better, hopefully,' Roberts said.
He had five birdies and two bogeys in a solid -- if not unspectacular -- third round. Funk pulled within two shots down the stretch, but Roberts restored his lead to three when he knocked a 167-yard approach to 3 feet at the 13th for his last birdie.
Roberts drove into the left rough at the 18th, then couldn't get his club down cleanly on the ball on the approach. He ended up short of the green, and his ball rolled back down the fairway.
'Wow, that didn't come out of there at all,' Roberts could be heard saying.
He was able to chip up to 5 feet, making the par-saving putt to preserve his three-shot lead on the steady Funk. Roberts is 1-3 with the 36-hole lead on the Champions Tour.
'I always thought that majors were important. Unfortunately I didn't get into enough of them on the regular tour,' Roberts said.
This is the final major championship of the season.
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