Tiger Woods and Lee Westwood go head to head with the world No. 1 spot at stake when the WGC-Bridgestone Invitational starts on Thursday.
Defending champion Woods -- he has won at Firestone in each of his last four trips and a PGA Tour record seven times in all -- is under threat from both Westwood and Phil Mickelson at the top of the world rankings.
Woods and Westwood were playing partners in the first two rounds of the British Open last year, with Westwood outscoring Woods by seven and going on to finish third while Woods missed the cut. They also played together, with Ernie Els as the third member of their group, in the first two rounds of the U.S. Open at Pebble Beach in June. In that case, Woods tied for fourth, with Westwood tying for 16th place, five shots worse.
They tee off at 1:50 p.m. ET, just ahead of Padraig Harrington and U.S. Open champion Graeme McDowell, who were also partners on the opening two days of the Irish Open last week.
Mickelson plays with McDowell's fellow Northern Irishman Rory McIlroy, the 21-year-old who pushed him into second place with a dazzling finish to the Quail Hollow Championship in May. They are among the early starters, teeing off at 9.50 a.m.
Mickelson could reach the No. 1 spot for the first time with a top-four finish, providing Woods is well down the field. But if Mickelson wins the tournament, there is nothing Woods can do to prevent the end of his latest five-year reign.
Westwood, runner-up in the Masters and British Open this season, has to finish first or second just to have a chance of overtaking the two Americans.