World Golf Championship, Akron, Ohio
Dates: 5-8 August Venue: Firestone Country Club Coverage: Leaderboard on BBC website, live on Sky Sports
FIRST ROUND LEADERBOARD: -6 B Watson (US) -4 P Mickelson (US), A Scott (Aus), G McDowell (NI) -3 C Campbell (US), R Goosen (SA), S O'Hair (US), J Overton (US), B Van Pelt (US) Selected others: -2 R Mcllroy (NI), P Casey (Eng) -1 P Harrington (Ire), E Els (SA), E R Fisher (Eng), L Glover (US), L Donald (Eng) +1 J Rose (Eng), L Westwood (Eng), R McGowan (Eng), +4 T Woods (US)
Woods is battling hard to avoid losing his world number one status
Bubba Watson fired a first-round 64 to lead the WGC-Bridgestone Invitational by two shots as Tiger Woods looked set to lose his world number one ranking.
Watson carded seven birdies with Phil Mickelson, Graeme McDowell, Kenny Perry and Adam Scott two behind, while Woods struggled with a four-over-par 74.
Mickelson will top the rankings with a win or a top-four finish in Ohio if Woods finishes outside the top 37.
Lee Westwood can also become number one but ended the day with a one-over 71.
England's Westwood, runner-up in two majors in 2010, would secure top status with victory this week with Woods outside the top two, and could also take top spot if he was second if Woods is worse than ninth and Mickelson fails to land the title.
Woods, a 14-time major winner and seeking a record eighth win at the Firestone Country Club, managed just two birdies in a round blighted by six bogeys, including four on the front nine.
In pursuit of his first PGA Tour title this season, Woods missed nine of 14 fairways and totalled 32 putts while recording his worst score at Firestone in 45 rounds.
After finishing the opening round 10 strokes behind fellow American Watson, Woods said: "I didn't play well. The only thing I did well is I kept my patience out there, grinded all day.
"That was the best I could have done. It's frustrating because I warmed up well, my practice sessions at home were good and it was not indicative of how I've been playing."
Woods, who recently returned to the game following a self-imposed five-month exile in a bid to repair his marriage, added: "I've just got to hopefully get it to even par or under par for the tournament and then hopefully put together a good weekend and see where that puts me."
Woods' 270-week reign as world number one is seriously under threat following Mickelson's efforts on Thursday, with the Masters champion bouncing back from two early bogeys with five birdies after the turn - including holing a lob wedge from 50ft on the sixth, his 15th hole - for an inward 30.
US Open champion McDowell was also an impressive performer with five birdies to finish just two shots off Watson.
"It's probably the best golf I've played since Pebble [Beach]," said the Northern Irishman, who tied for 23rd alongside Woods at the Open three weeks ago. "I've been a bit under the radar this week."
The left-handed Watson, who earned his maiden PGA Tour win at the Travelers Championship in June, made a steady start but then secured four successive birdies before dropping his only shot of the round at the 15th.
"I knew it was going to be tough but I putted really well, hit good iron shots and made it look a little bit easy," said the 31-year-old. "But we're not done yet. We've still got three tough days of golf to go."
The big-hitting Watson is 17th in the Ryder Cup standings, with the top eight players at the end of next week's US PGA earning automatic spots on the team for October's match in Wales.
"I'd give up my win to play the Ryder Cup. That's how much it means to me," said Watson, who took just 22 putts at Firestone.
Rory McIlroy, Paul Casey and Frenchman Gregory Bourdy are four shots off the pace, with three-time major winner Padraig Harrington carding a 69, Luke Donald and Ross Fisher 70s and Justin Rose a 71.
The field in the event, which has no halfway cut, includes the top 50 players in the world.