Ted Purdy, Tommy Tolles and Robert Gamez posted matching rounds at 7-under 65. That trio shares second place at 15-under-par 201 with John E. Morgan (68) and Notah Begay III (66).
Due to bad weather in the forecast, Sunday's tee times have been moved up. The players will be paired in threesomes and will tee off both the front and back nines.
Byrd, who led by one shot entering the round, burst out of the gate with three straight birdies from the first to move to minus-15. After a par at the fourth, Byrd stumbled to a bogey at the fifth at En-Joie Golf Club.
Byrd, the 2002 Buick Challenge winner, erased that mistake with a birdie at the ninth. Around the turn, he posted six straight pars before a birdie at the 16th got him to minus-16. He parred his final two holes to maintain his lead.
'I thought we were going to run away with it,' said Byrd of his and Morgan's early birdie spurts. 'We probably jinxed ourselves. We said, 'Let's just keep playing like this and we'll have a match-play match tomorrow.''
Morgan, who could have made this week's British Open with a win last week, lost the John Deere Classic in a playoff. He put himself into good position this week though, posting just three bogeys over the first 54 holes.
In the third round Saturday, Morgan sank four straight birdies from the second to move to 15 under. That run ended harshly as he dropped shots with back-to-back bogeys from the sixth. He atoned for those errors with birdies on the 12th and 16th to share second place.
Purdy began the day four strokes behind Byrd, but erased that deficit before Byrd teed off. Purdy eagled the third and fifth, both par-5s, to jump to minus-12.
He collected birdies at seven and 12 to get to 14 under. Purdy, who is looking for his first tour win, picked up another birdie at 15, but dropped a stroke on 17. He closed with a birdie at the last to join the crowd at 15 under.
Tolles, who is also looking for his first tour win, birdied the first and fourth, but double bogeyed the second. He picked up birdies at the seventh and ninth to make the turn at minus-10. After a birdie at the 12th, Tolles ran off three straight birdies from the 14th. He then closed his round with a birdie at the last.
'I think the split tees are going to make a big effect,' said Tolles. 'A lot of the leaders are going to be going off at the same time or fairly close to guys who are four, five and six shots back. Everybody will be within six or seven holes of each other, so you're going to have the leaders playing very aggressive because they know that guys just a couple of groups in front of them can really put a hurting on the golf course. There won't be conservative play by anybody.'
Gamez, a two-time winner on tour, birdied the first, but stumbled to a bogey on No. 3. He then drained four consecutive birdies from the third to get to 12 under. Gamez, who made six straight birdies en route to a second-round 61, birdied the par-5 12th. He then joined the group at minus-15 with back-to-back birdies from the 16th.
'The old me probably would have shot 80 the second day, but I've been playing extremely well, so my first round didn't bother me at all,' said Gamez, whose last win came in 1990. 'Yes, I was frustrated with the score because I felt I should have shot no worse than 2 or 3 under. But I didn't make any putts. It was just one of those things.'
Begay spread three birdies over his first nine holes. On the back side, he faltered to a bogey at the 10th. But the four-time tour winner reeled off three straight birdies from the 12th before getting to minus-15 with a birdie on No. 16.
Craig Stadler, the defending champion, managed just a 1-under 71. He slid to a share of 32nd place at 9-under-par 207.