Howell had been one shot adrift after his first round

Charles Howell III holds a one-shot lead in the USPGA Tour Championship in Atlanta.

The 23-year-old, who is the youngest player in the field, struck a one-under-par 69 to lie at five under after 36 holes.

Breathing down his neck are Steve Lowery, Len Mattiace, Vijay Singh and David Toms.

Howell, the reigning PGA Tour Rookie of the Year who captured his first career title three weeks ago at the Michelob Championship, had begun the day one shot behind overnight leaders Singh and Lowery.

Mattiace would have been level with Howell but for an unlucky bogey on the final hole.

His third shot out of a bunker 40 yards from the pin hit a tent just behind the green.

It then bounced back 50 feet in front of the green.

Mattiace recovered well to chip to four feet and putt out but it cost him a crucial shot.

Tiger Woods is four shots off the pace after shooting a two-under-par 68.

Among those tied with Woods in joint ninth is world number two Phil Mickelson.

Only 12 of the 30-man field are under par at the halfway stage.

Scores after the second round of the USPGA Tour Championship (US unless noted):

135 Charles Howell III 66 69
136 David Toms 70 66, Len Mattiace 68 68, Steve Lowery 65 71, Vijay Singh (Fiji) 65 71
138 Chris DiMarco 70 68, Retief Goosen (South Africa) 69 69, Fred Funk 67 71
139 Tiger Woods 71 68, K.J. Choi (South Korea) 71 68, Phil Mickelson 70 69, Scott McCarron 70 69
140 Jerry Kelly 71 69, Kenny Perry 71 69
141 Nick Price (Zimbabwe) 73 68, Chris Riley 72 69, Bob Estes 72 69, John Rollins 70 71, Jim Furyk 68 73, Shigeki Maruyama (Japan) 68 73
142 Ernie Els (South Africa) 73 69, Davis Love III 72 70, Loren Roberts 71 71, Rich Beem 70 72
143 Robert Allenby (Australia) 74 69
144 Jeff Sluman 72 72, Justin Leonard 71 73, Sergio Garcia (Spain) 71 73
145 Jose Maria Olazabal (Spain) 74 71
147 Rocco Mediate 74 73