By Mark Lamport-Stokes
LOUISVILLE Kentucky (Reuters) - Four-times winner Tiger Woods, pain-free after suffering a back scare on Sunday, prepared for an early morning start as the 96th PGA Championship began under clear skies at Valhalla Golf Club on Thursday.
Woods, who clinched the most recent of his PGA Championship titles in 2007, was scheduled to begin his opening round from the 10th at 8:35 am EDT on a challenging course that measures 7,458 yards off the back tees.
American club professional Brian Norman found the right side of the fairway with the opening shot of the tournament at the par-four first, before being followed by Scotland's Russell Knox and American Roberto Castro.
Tall Swede Robert Karlsson, American Frank Esposito and Japan's Koumei Oda launched proceedings in the year's final major at the par-five 10th hole on the hilly, par-71 layout at Valhalla.
Woods, hunting his 15th major crown but first since the 2008 U.S. Open, has been grouped with former champions Phil Mickelson and Padraig Harrington for the first two rounds in a threesome that will attract the biggest galleries out on the course.
The American's fitness for the PGA Championship had been in some doubt after he was forced to withdraw midway through the final round of the WGC-Bridgestone Invitational at Firestone Country Club in Akron, Ohio on Sunday.
However, he said the problem was resolved when his sacrum (a bone at the base of the spine), which had popped out after he landed awkwardly in a bunker at Firestone, was put back in by his physiotherapist.
"My sacrum went out, it pinched the nerve and hence the spasms," Woods told reporters on Wednesday after he ended days of speculation over his fitness by arriving at Valhalla to play nine holes in practice.
"Once the bone was put back in, it was all good. The spasms went away and I started to get some range of motion. I'm not in any pain. That is the good part."
In keeping with tradition, this season's first three major winners have been grouped together for the first two rounds - American Bubba Watson (Masters), Germany's Martin Kaymer (U.S. Open) and Northern Ireland's Rory McIlroy (British Open).
Watson and company were set to start on the first tee from 1:45 p.m.
World number two Adam Scott of Australia will play with Englishman Lee Westwood and American Jordan Spieth while Jason Dufner will start his title defense in the company of two other former champions, fellow American Keegan Bradley and South Korean Yang Yong-eun.
In other high-profile groups, English world number five Justin Rose, American Matt Kuchar and South African Louis Oosthuizen will play together while third-ranked Spaniard Sergio Garcia has been drawn with American veteran Steve Stricker and U.S. Ryder Cup captain Tom Watson.
The PGA Championship has, in recent years, enjoyed the strongest field of the four majors and 99 of the world's top 100 players are chasing the season's final grand slam title this week.
Weather forecasts predicted a chance of isolated showers later on Thursday with scattered thunderstorms likely on Friday and Saturday.
(Reporting by Mark Lamport-Stokes; Editing by Justin Palmer)