Rory Sabbatini carded a 6-under 65 to move into a share of second at 11-under-par 202. He is joined there by Cameron Beckman, who shot a third-round 66. Tom Byrum and Luke Donald are one stroke further back at minus-10.
Roberts began his round at Westchester Country Club five strokes behind overnight leader Fred Couples. Roberts opened with a lengthy birdie putt at the par-3 first. He settled down with four consecutive pars from the second.
The eight-time winner on the PGA Tour stuck a wedge within 2 feet of the cup at the sixth for his second birdie. Roberts came back at the very next hole with a 5-foot birdie putt to move to minus-8.
The 48-year-old Roberts, who has won five of the seven events he has held the 54-hole lead, faltered to a bogey at the eighth, but caught fire around the turn to climb to the top of the leaderboard. He birdied the 10th and then sank a 6-foot birdie at the 11th.
After a par on No. 12, Roberts dropped his second shot within 6 feet of the hole at the 13th. He converted that birdie try to get to 10 under and a share of first.
Roberts knocked a wedge to 18 feet at the 17th to set up his seventh birdie of the round. He was not finished either. His second shot to the par-5 18th came to rest on the front edge of the green. Roberts two-putted for birdie for a back-nine 30.
'I've been working on my golf swing, struggling with my game a little bit, and working on my golf swing real hard, in fact still working on a lot this week,' said Roberts, whose last win was at the 2002 Texas Open. 'I was working on it about every shot on the golf course today. I just happened to hit it good.'
Sabbatini was tied with Roberts to start the round and also picked up a birdie at the first. The South African dropped in back-to-back birdies from the fifth to get to 8 under.
The 2003 Capital Open winner drained consecutive birdies from the 10th to grab a share of the lead. Sabbatini ran off five pars in a row and was passed by Roberts. Sabbatini birdied the 17th to get within one shot of the lead and cap the lone bogey-free round of the day.
'Obviously I've been driving the ball well, but I think there's some work to be done with my irons,' said Sabbatini. 'I'm obviously not getting the ball close enough to the hole. I've been putting more focus on putting the ball on the surface than trying to hit it close every hole.'
Beckman stumbled to a bogey at the third, but came back to birdie No. 5. He notched his second birdie at the 10th, but tripped to another bogey at 13.
Beckman, the 2001 Southern Farm Bureau Classic winner, dropped his tee shot within 7 feet to set up birdie at the 14th. He chipped in at the next to make it back-to-back birdies
The 34-year-old then sank a 10-foot birdie try at the 16th. He chipped in for birdie at the 17th. Beckman closed out a run of five straight birdies as he drained a 20-footer at the last.
'I had three chip-ins, which for me is nice in the last five holes. Basically I wasn't doing much and birdied the last five, so it was nice,' said Beckman. 'I've chipped in four times this week, and I haven't chipped in four times all year, so it's been nice. It's been a big change.'
Vijay Singh posted an even-par 71 to remain at minus-9. He is joined there by Padraig Harrington, who shot a 3-under 68. Sergio Garcia is one stroke behind that duo at 8-under-par 205.
Couples, the overnight leader, struggled to a 3-over 74. He fell to 7-under-par 206 and shares ninth place with Kris Cox, Brian Gay, Dennis Paulson and Masters champion Phil Mickelson.
Jeff Sluman, the 1988 PGA Championship winner, made the cut at minus-4, but was disqualified during the third round. He informed a tour official he teed of the first hole with a ball that was incorrectly marked.
The tour official then went to confirm the ruling. As he did, Sluman bogeyed the third, but eagled the fourth. At that point, the official returned and Sluman was told he was disqualified from the event.