Brett Quigley fired a 6-under 64 and Patrick Sheehan posted a 3-under 67 to match Franco at 10-under-par 200.
Defending champion Kenny Perry got in the hunt on Saturday at Brown Deer Park Golf Club. He is alone in third place at 9-under-par 201, one ahead of Jason Dufner (68) and Scott Verplank (67).
Franco held the lead throughout much of Saturday's third round, but did not play particularly well. He drained a 3-footer for birdie at the sixth, then chipped in from the fringe behind the green at the eighth.
Franco three-putted for bogey at the 11th, but had a good look at birdie at 13 after driving into the rough. He missed the 5-footer for birdie, but made a couple of pars at 14 and 15, including a save from the right trees at the par-5 15th.
The 39-year-old from Paraguay hit an iron off the tee at 16, but found the left side of the fairway, bringing a tree into play. He wedged his shot over the tree and stopped it 15 feet from the hole, where he converted the birdie try.
Franco was 11 under par when he drove way left into trees. He pitched back into the fairway and played his third to 25 feet. Franco made the putt for par, but had no such luck at 18.
This drive went right into trees, but he had an opening. Franco tried to run a 2-iron up the fairway, but settled in thick rough short and left of the green. Franco's pitch went only a few yards and his fourth went 25 feet past the hole.
Franco missed the par-saving putt and found himself in a tie for the lead.
'That's unbelievable,' said Franco, a three-time winner on the PGA Tour. 'I forgot about my focus, but still, 10 under is not bad. I need to shoot a low score tomorrow if I want a chance to win.'
Franco might have the edge come Sunday thanks to his success here in 1999, but the very fact that he has won on tour gives him an advantage over his fellow co-leaders.
Quigley, whose best finish on tour was a tie for second in Greensboro three years ago, tallied three birdies on his front nine. He hit a 7-iron to 10 feet from 198 yards at the par-3 14th which set up his fourth birdie of the round.
At the 15th, Quigley drove into the rough and was forced to lay up short of the putting surface. His third rolled 2 feet from the hole, where he tapped in for birdie to go to minus-9.
Quigley played a spectacular second to the 18th that left him with 15 feet for eagle. His putt broke toward the hole, but he tapped in for birdie and his second career piece of the 54-hole lead.
'Today, I tried to take the weekend like I did the first two rounds, be really patient with myself and just go play golf,' said Quigley, who shared the third-round lead at the 2001 Colonial en route to tying for fifth.
Sheehan made his move up the leaderboard with Quigley in the clubhouse and Franco in the final pairing. Sheehan made the turn at even-par 34, but got going with a 25-foot birdie putt at the 12th. He birdied 13 for two in a row and nearly took the outright lead at the par-5 closing hole.
Sheehan, 34, nearly pitched in from off the green, but settled for birdie and a share of the lead.
'I grew up on courses like this in Rhode Island,' said Sheehan, whose best finish this season was a tie for third at the Heritage. 'They're not very long. Fairways and greens, that's the trick out here.'
Scott Hoch, a two-time champion, managed an even-par 70 and is tied for seventh place with Billy Andrade (67), Brian Gay (67), Fred Funk (67), Jay Williamson (68), Danny Briggs (68) and Olin Browne (68). That group is knotted at 7-under-par 203.
Rich Beem, the 2002 PGA Champion, was in second place at the start of Saturday's third round. He struggled to a 6-over 76 and is tied for 33rd place at minus-2.