LOUISVILLE (AFP) - Defending champion Jason Dufner, who has been battling a nagging neck injury, withdrew from the 96th PGA Championship after only 10 holes of his opening round Thursday.

The 37-year-old American who outdueled Jim Furyk in last year's final round at Oak Hill to win his first major title was eight-over par through 10 holes when he decided to pull out.

Dufner, who stands in position to qualify for the US Ryder Cup team, had been troubled by bulging neck discs that limited his head and shoulder mobility.

After starting with a double bogey and following with bogeys at the second and third holes, Dufner took a bogey at the sixth and endured a triple-bogey nightmare at the par-5 10th that pushed him to walk off the course.

Dufner becomes the latest setback for the US Ryder Cup team that will try to reclaim the trophy from Europe next month at Gleneagles.

He stood eighth in the points chase entering the year's final major at Valhalla, the last qualifying event for the US roster.

The Americans also saw Matt Kuchar, assured a berth on qualifying points, withdrew Thursday with back spasms.

And Tiger Woods withdrew from an event last week with back spasms and is barely back from a layoff of nearly four months following back surgery to ease a pinched nerve.