By Mark Garrod, PA Sport Golf Correspondent, Rochester

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Get prepared for another big shock in major championship golf.

A month after world number 396 Ben Curtis produced the greatest upset in Open history, world number 169 Shaun Micheel and Chad Campbell, 58th but hardly a household name, share the lead going into the final round of the United States PGA at Oak Hill in Rochester, New York.

And unlike Curtis at Sandwich they do not have to worry about world number one Tiger Woods coming at them.

Woods is heading for his worst finish in a major since he turned professional in 1996 after a third-round 73 left him 13 strokes adrift.

He lies joint 43rd of the 70 players who had survived the halfway cut. His worst finish in a major as a pro is 29th - both at the US PGA in 1997 and two years ago.

Micheel, two ahead overnight, had still to tee off when Woods finished, but when the Orlando player without a single US Tour win to his name resumed with a bogey many might have expected him to continue a downward slide.

Instead, however, he seemed to take inspiration from Curtis' amazing performance in his first-ever major and went four clear.

A hat-trick of birdies from the seventh opened up a three-stroke gap on the chasing pack, then he birdied the 372-yard 12th as well and holed from 15 feet for par at the next after a lady spectator had bizarrely picked up his ball when he flew the green from a fairway bunker.

Micheel, who is playing only his third major and his first US PGA, was close to a hole-in-one at the 181-yard 14th as the dream ride continued, but he was not quite out of sight of all of the chasing pack.

Fellow American Campbell, who missed the halfway cut in the first five of his eight majors but is being tipped for great things by tour insiders, finished birdie-birdie-bogey-birdie for a best-of-the-week 65.

And as soon as that was posted Micheel started to creak.

Previously best known for rescuing an elderly couple from a sinking car 10 years ago, Micheel still had a firm grip on things, but that went when he bogeyed the last three holes for a 69 and matching four under aggregate of 206.

Masters champion Mike Weir is in third place at one under following a 70, while South African Tim Clark is one further back.

Germany's Alex Cejka is among those who need Micheel and Campbell to feel the heat and buckle over the final 18 holes to have a chance.

Now a member of the US circuit after coming through the qualifying school last September, the former Volvo Masters champion rolled in an 18-foot downhill birdie putt on the last - a 482-yard par four - to complete a 68 for a one over par aggregate of 211.

He is joint fifth with Ernie Els, Briny Baird and Billy Andrade.

"That was very great," said Cejka. "I played good all day long and it's always nice to finish with a birdie, especially on a hole as tough as that.

"I missed only one fairway and my ball-striking was suddenly there. I'll just try to do the same tomorrow. If you keep the ball on the fairway it makes the rest a little bit easier."

Woods has not broken par all week and never looked like doing so from the moment he teed off.

Bogeys at the first two holes were both the result of drives into the thick rough and when another, with a three-wood, dived into heavy rough again on the seventh Woods slammed the club back into the bag. He had yet to find a fairway off the tee.

As on the first and second holes, he had no hope of making the green and his chances of lifting his first major since the United States Open in June last year receded further.

He finally made a fairway at the ninth, only to bogey that as well to be out in a four-over 39. The birdies then came at the 14th and 15th, but short of the green in two at the 482-yard par four last he chipped over the green and dropped back to nine over.

"I've just been a touch off," said Woods. "I've putted well, but par putts are not going to get it done. If you are a little off here that's it."

He had no criticism for the set-up of the 1995 Ryder Cup course - but he did for Carnoustie at the 1999 Open.

"This is the hardest fairest course we've ever played," he commented. "Carnoustie was not fair. That's one fantastic course, but they just did not set it up fairly." He finished 10 over par there - and was seventh!

"I've fought on every shot," added Woods. "If I had bagged it (slang for giving up) I could have shot a million."

Ireland's Padraig Harrington, meanwhile, recovered from a scrappy start to shoot 69. But having survived the halfway cut with nothing to spare at eight over he was still only seven over.

Playing partner Gary Evans had a 71 for nine over, the same as Ian Poulter (72), while Paul Casey dropped three shots in the last two holes for a 75 and 13 over aggregate.

Leading British and Irish player at halfway was Luke Donald on five over and with four to play he had improved to four over and joint 25th. But then came a hat-trick of bogeys from the 15th before he matched Cejka's birdie at the last for a 71 and six over total.

Collated third-round scores (USA unless stated, par 70):

206 Chad Campbell 69 72 65, Shaun Micheel 69 68 69

209 Mike Weir (Can) 68 71 70

210 Tim Clark (Rsa) 72 70 68

211 Briny Baird 73 71 67, Alex Cejka (Ger) 74 69 68, Ernie Els (Rsa) 71 70 70, Billy Andrade 67 72 72

212 Charles Howell 70 72 70, Vijay Singh (Fij) 69 73 70, Fred Funk 69 73 70

213 Hal Sutton 75 71 67, Jay Haas 70 74 69, Robert Gamez 70 73 70, Loren Roberts 70 73 70, Phil Mickelson 66 75 72, Tom Pernice 70 71 72, Rod Pampling (Aus) 66 74 73, Adam Scott (Aus) 72 69 72

214 Woody Austin 72 73 69, Kevin Sutherland 69 74 71, Toshimitsu Izawa (Jpn) 71 72 71, Frank Lickliter 71 72 71, Lee Janzen 68 74 72, Tim Herron 69 72 73

215 Jim Furyk 72 74 69, Carlos Franco (Par) 73 73 69, Scott McCarron 74 70 71

216 Luke Donald (Gbr) 73 72 71

217 Padraig Harrington (Irl) 72 76 69, Peter Lonard (Aus) 74 74 69, Kenny Perry 75 72 70, Rocco Mediate 72 74 71, Niclas Fasth (Swe) 76 70 71, JL Lewis 71 75 71, Fred Couples 74 71 72, Duffy Waldorf 70 75 72, Jesper Parnevik (Swe) 73 72 72, Todd Hamilton 70 74 73

218 Bob Burns 72 76 70, David Toms 75 72 71, Stuart Appleby (Aus) 74 73 71

219 Gary Evans (Gbr) 74 74 71, Angel Cabrera (Arg) 71 76 72, Ian Poulter (Gbr) 72 75 72, Jonathan Kaye 74 73 72, Tiger Woods 74 72 73, Aaron Baddeley (Aus) 69 77 73, Len Mattiace 74 70 75, Geoff Ogilvy (Aus) 71 71 77, Jose Coceres (Arg) 73 68 78

220 Robert Allenby (Aus) 70 77 73, Bob Estes 71 78 73, Shigeki Maruyama (Jpn) 75 72 73, Scott Hoch 75 72 73, Mark Calcavecchia 73 71 76

221 Rory Sabbatini (Rsa) 71 75 75, Trevor Immelman (Rsa) 74 70 77, Phil Tataurangi (Nzl) 72 71 78

222 Bernhard Langer (Ger) 75 72 75, Joe Durant 71 76 75, Ben Crane 73 73 76

223 Brian Gay 74 74 75, Paul Casey (Gbr) 79 69 75, Chris DiMarco 74 71 78

224 Jose Maria Olazabal (Spa) 74 74 76, Eduardo Romero (Arg) 77 71 76

225 Michael Campbell (Nzl) 74 71 80

226 Billy Mayfair 76 72 78

228 KJ Choi 74 74 80