Steve Jones, the 1996 U.S. Open champion, who is currently ranked 743rd in the world, fired an 8-under-par 64 to take a one-shot lead at the TPC at Sawgrass.
The Big Four posted mixed results on Thursday.
Vijay Singh, the No. 1 player in the world, carded a 5-under 67 and is part of a group tied for eighth place.
Tiger Woods and Phil Mickelson, ranked second and fourth, respectively, each posted rounds of 2-under-par 70. They are part of a logjam tied for 30th place.
Sawgrass took in a lot of water with storms this week and Woods suffered several times with mud on his ball. He was 2 under on the front nine, but recorded two bogeys and two birdies on his second nine, the front side at Sawgrass. Woods closed with an 8-foot birdie putt at his last.
'I missed some short birdie putts I probably should have made, and I just tried to get by with some mud balls out there,' said Woods, who won this title in 2001.
Mickelson had a much more erratic round. He birdied four of his first six holes, then dropped two shots with a double bogey at the par-3 eighth. Mickelson collected two more birdies at 11 and 12, but finished with three bogeys and one birdie in his last four holes, including an ugly drive at 18 that found the water.
'If you had given me 2 under I would have taken it gladly at the start of the round because I knew I was susceptible to a couple of squirrely shots,' said the reigning Masters champion.
Ernie Els, No. 3 in the world, mixed three birdies and two bogeys for his round of 1-under 71. He is tied for 51st.
These superstars are looking up at one of the most unlikely leaders possible.
Jones opened on the back nine Thursday and parred his first six holes. He tapped in a short birdie putt at the par-5 16th, then made it two in a row at the 17th. Jones hit a poor 7-iron into the 18th green, but drained the 60-footer to keep the birdie streak going.
Jones, who served as one of Hal Sutton's assistant captains at last year's Ryder Cup, two-putted for birdie at the second. He hit a 7-iron to 12 feet to set up birdie at the third, but caught an unlucky break at four. Jones' drive landed in a sand-filled divot, but he choked down on a pitching wedge from 90 yards out and stopped it a foot from the hole.
'That was a big turning point, because that could have been an easy bogey or double from that lie,' admitted Jones.
The 46-year-old tallied his fourth consecutive birdie at the fifth. Jones' 20- footer found the bottom of the cup after allowing for 12 feet of break. He missed an 8-foot birdie try at the sixth, but the former U.S. Open champion had one left in him.
At the ninth, Jones knocked a 9-iron to 10 feet and converted the putt for his two-shot lead.
'I was just really patient today and I knew a couple under would be a good score,' said Jones. 'I didn't pressure it much. I felt pretty good coming into this week.'
Jones hasn't felt good in some time. He missed all of the 2004 season with an injury to his elbow where the tendon was off the bone. Jones tried rehab, but eventually needed surgery.
At 46 and coming off a serious injury like his, Jones had some deciding to do about how serious he was about rejoining the PGA Tour. His last top-10 finish was at the rain-shortened BellSouth Classic in 2000, when he tied for fifth.
Jones regained some of his desire assisting Sutton at Oakland Hills, but a talk with Champions Tour star and fellow University of Colorado alumnus, Hale Irwin, got Jones back on track.
'The main thing he wanted me to do is to be positive, don't be a complainer,' said Jones. 'You have to ask yourself, do you really want to do this anymore. And I told him I do. And then we went into some other stuff, and that's just for him and I.'
Funk and Johnson played together on Thursday and combined for 15 birdies and one bogey. Johnson dropped a shot at the 15th, while Westwood was flawless in the first round.
European Ryder Cup partners Luke Donald and Sergio Garcia shot matching rounds of 6-under 66 and were joined by J.L. Lewis in a tie for fifth place.
Padraig Harrington, who has been the runner-up the last two years, posted a 67 to join Singh, Brett Quigley, Bob Estes and Bob Tway in a share of eighth place.
Defending champion Adam Scott opened with a 3-under 69 and is tied for 20th place.