Gronberg shot a six-under par round of 66

Sweden's Mathias Gronberg fired five birdies on the back nine to grab the lead after Thursday's first round of the PGA International in Ohio.

Under the event's scoring system, Gronberg, 36, finished with 13 points.

That gave him a two-point lead over Australians Stuart Appleby and John Senden and US veterans Stewart Cink and Tom Pernice.

Britain's David Howell and Justin Rose are four points off Gronberg's pace at the Castle Pines Golf Club.

The scoring system sees golfers receive eight points for an albatross, five for an eagle, two for a birdie, zero for par, minus-one for a bogey and minus-three for anything worse.

Gronberg, ranked 265th in the world, said: "I found my game on the driving range and had a very good day."

Masters champion Phil Mickelson, who defends the PGA Championship title next week, struggled to one point with a 73.

Cink hopes to make the US Ryder Cup team but must improve 10 spots in the next 10 days to reach the automatic list.

He made an eagle at the par-five first hole and added three birdies.

"Hopefully I can have a few more rounds like and get it taken care of," said Cink, who was one of Hal Sutton's captain's picks two years ago.

Appleby, looking for a confidence boost ahead of the year's final major, got one at the 14th hole when he sank a 70-foot bunker shot for an unlikely eagle.

"That's the beauty of this format - it's very dramatic," he said.