After three consecutive rounds of 65 on three separate courses, Byrum stumbled to a fourth-round 3-under-par 69. Andrade, who began the day two shots back of Byrum, fired a bogey-free 67 to tie his counterpart at 24-under-par. Scott McCarron is just one off the 72-hole lead following a 66. Shaun Micheel tied the low round of the tournament, a 9-under-par 63, to climb to within two shots of Byrum.
Playing on the host course, the TPC at Summerlin, Byrum appeared to be headed for another spectacular round. The 15-year Tour veteran birdied three of his first four holes, and then added a fourth red number at the par-3 8th to move four strokes clear of the field at 25-under-par.
Following a bogey at the par-5 9th, Byrum steadied himself with four straight pars on the back nine, before regaining his form with a birdie at the 14th. Byrum carded his sixth, and final birdie of the day at the 16th to move to 26-under, but limped home bogey-bogey.
After making a 25-foot birdie putt at the 16th, Byrum three-putted the 17th and made a poor chip from off the green on the 18th.
'I just lost my feel,' said Byrum following his 5 -hour round. 'There was a little fatigue, and maybe my confidence went. I think I'll feel fresher tomorrow. It was hard to concentrate and focus on what I needed to do out there.
'But I'm still tied for the lead and have a chance to win the tournament. So I'm very happy about that.'
This is the first time Byrum has held at least a share of the lead entering the final round of a PGA Tour event since the 1989 Kemper Open. He went on to win that tournament for his first, and thus far, only Tour triumph.
All of the top- four players on the leaderboard are in dire need of a good finish this week. Byrum stands in 125th place on the money list. Andrade sits in the 159th position. McCarron is currently 123rd, while Micheel resides in 130th place.
The top 125 by season's end earn their 2001 PGA Tour playing privileges. There are two full-field events remaining after this week.
Next week, Phil Mickelson and Stewart Cink will be representing their country at the Presidents Cup in Lake Manassas, Va. This week, they're fine-tuning their games in Las Vegas.
Mickelson carded a Saturday 66 to move to 21-under-par for the tournament, three shots off the lead. Cink is just four back following a fourth-round 7-under-par 65. At 20-under, Cink is tied with Blaine McCallister for 6th place.
'If I can get to eight, nine or 10 under tomorrow, I might have a good shot,' Mickelson said.
It might not even take that.
Said Byrum: 'I wouldn't be surprised if (Andrade and I) were sitting there watching each other and somebody blows by us.'