Jay Haas, who held the lead through a good portion of the third round, matched Montgomerie's 67 and stands at 11-under-par 202. Jim Furyk also posted a 67 to join Haas in second place, while tournament host Tiger Woods recovered from a tough start to card a 69 to also finish at minus-11.
Miguel Angel Jimenez, who posted five worldwide wins in 2004, fired a third-round best 5-under 66. He stands alone in fifth place at 10-under-par 203, while Irishman Padraig Harrington is one stroke further back at minus-9.
Haas began the round two strokes behind Montgomerie. The 51-year-old Haas closed the gap with birdies at the second and third. Monty however remained one stroke ahead of Haas as he birdied the second.
Haas briefly tied Montgomerie in the lead when he birdied the par-5 fifth. Montgomerie also birdied the hole to move one shot clear of Haas. But, Haas showed his determination as he came right back with a birdie at the sixth to tie Monty in the lead at minus-11.
Montgomerie hit a poor tee shot at the ninth and it led to his only bogey of the round. That dropped in him one behind Haas.
Haas, whose last win came at the 1993 Texas Open, moved two strokes ahead of Montgomerie when he two-putted for birdie at the par-5 13th at Sherwood Country Club. However, Haas hit a poor bunker shot at the next and that led to a bogey, which drooped him back to minus-11.
Meanwhile, Montgomerie was biding his time with six consecutive pars from the 10th. That run included a solid par at 11. He had to punch his second shot out from underneath a tree. He then stuck his third shot from 210 yards out to 3 feet and rolled home the par putt.
At the par-5 16th, the Scotsman dropped his second shot nine feet from the cup. He sank that eagle putt to move one stroke ahead of Haas at minus-12.
Montgomerie, who was one of four sponsor's exemptions, then drained a 7-foot birdie putt at the 17th to climb to 13 under. He parred the last.
'It's all on tomorrow. Tiger's birdie at the last sets up a very good finish tomorrow,' said Montgomerie, whose only win in the United States came at the 2000 Skins Game. 'There's only two shots between the first four guys and that's nothing around here. Sunday will be a good challenge for me.'
Haas parred his final four holes to remain at 11 under.
Woods got off to a rough start as he bogeyed the first, but bounced back with a birdie at No. 2. He then stumbled to a double bogey at the third and a three-putt bogey at the fourth to fall back to minus-6.
The tournament host recovered with birdies at five and nine to move back into contention. Woods kicked in a 3-foot birdie putt at 13 and came back with a two-putt birdie at the 16th. Woods closed with a 9-foot birdie at the last to share second place.
'I missed a couple short putts early on, but I figured there were a lot of holes to play,' Woods said. 'I had been playing well all week, so I figured I'd keep doing what I had been doing and try not to play hockey on the greens. It's going to take a good number to win tomorrow and I need to get off to a better start for that to happen.'
Furyk closed with a strong rally after a tough front nine. The 2003 U.S. Open champion birdied the par-5 second for the third straight round. His troubles began at the next as he double bogeyed the third.
Furyk faltered to a bogey at the fourth to drop back to 5 under. He rallied with birdie on five and seven, but tripped to another bogey at the ninth.
The 34-year-old settled down with three straight pars. Furyk then caught fire as he ran off three consecutive birdies from the par-5 13th.
Furyk moved to 10 under with a birdie on 17 and joined the crowd in second place with a 10-foot birdie putt at the last.
'I hit the ball well on the front, but just got some bad breaks,' said Furyk. 'The back nine was the exact opposite as I took advantage of all of my opportunities and got a few very fortunate bounces that helped me out.'
Chris DiMarco posted a 1-under 70 and is alone in seventh place at 7-under-par 206. Chad Campbell, the 2003 Tour Championship winner, stands one stroke further back at minus-6.
Stewart Cink is alone in ninth place at 5-under-par 208 with Fred Couples one shot behind him. Defending champion Davis Love III stumbled to a 3-over 74. He fell into 11th place at 3-under-par 210 with world No. 1 Vijay Singh one stroke back at 2 under.
Kenny Perry is in 13th at 2-over-par 215 with British Open champion Todd Hamilton one stroke behind him at plus-3. Stephen Ames and John Daly share last place in the 16-player field at 4-over-par 217.