Tom Pernice, Jr. posted a 6-under 66 to finish alone in third place at 10-under-par 206.
'Until I signed my scorecard, I had no idea what I did,' said Janzen. 'That's a sports psychologist's dream, is for a player to tell him he didn't know he made those birdies.'
Janzen, who has gone winless on the PGA Tour for the last five years, began the day tied for the lead with Tway at the TPC at Sugarloaf as morning rain softened the greens. After a bogey at the fifth, Janzen found himself battling for position with the likes of Tway and Pernice throughout the round.
'I was just playing one shot at a time,' said Janzen. 'I certainly didn't have the groove I had the first two days. I was just trying to survive.'
The 38-year-old birdied the sixth and added a birdie at the 10th to keep pace at 9-under. Janzen hit a bunker shot to four feet for a birdie at the par-4 13th landed his second shot inside two feet at the 15th. He drained the birdie putt to join Tway in the lead at minus-11.
At the par-4 17th, Janzen left his approach within five feet of the cup for another birdie. Meanwhile, Tway found a greenside bunker at the very same hole en route to a bogey and a two-shot swing.
Tway birdied the par-5 18th for a round of 69 but Janzen matched him with a birdie of his own to maintain a two-shot advantage.
'Today I struggled early and hung in there and kept myself in there and ended up hitting good shots on the back to make some birdies,' said Janzen. 'So I can remember that tomorrow no matter how I'm playing, that all I got to do is hang in there and maybe at the end I'll have a chance.'
The two-time U.S. Open champion has put himself in contention for his first PGA Tour title since his victory at The Olympic Club in 1998.
'It would be really exciting,' said Janzen. 'All I can do is go out there and give it the old college try and play my hardest.'
Tway played steady golf throughout the day. He birdied the third and added a birdie at the 10th to dictate the pace until late in the round. Tway drained a nine-foot putt for a birdie at the 13th before his only blunder of the day at the 17th hole.
'I know tomorrow that I need to go out and shoot a good round, and I'll kind of have that in mind,' said Tway, who is searching for his first title since 1995. 'I'm excited about tomorrow.'
Hank Kuehne, the 1998 U.S. Amateur champion, had a wild round at Sugarloaf. The hard-hitting 27-year-old carded a 67 that featured an ace at the par-3 second, six birdies and three bogeys. Kuehne finished at 9-under-par 207, one shot clear of J.J. Henry and Billy Andrade.
Ben Crane fired the low round of the tournament with a bogey-free 64, one stroke shy of the course record. Crane was joined by Stewart Cink, Olin Browne, John Rollins, Brenden Pappas and Esteban Toledo at 7-under-par 209.
Jay Williamson finished alone in 13th at 6-under-par 210 followed by a large group at minus-5 that includes Fred Couples, Paul Lawrie and Chris DiMarco.
Defending champion Retief Goosen was one shot further back in a group at 4- under-par 212.