AUGUSTA, Mo. (AP) _ Rocky Thompson put a recent short-game lesson to good use in the first round of the Boone Valley Classic.

Thompson, 57, a three-time winner on the Senior PGA Tour, shot a bogey-free 6-under-par 66 on Friday to take a one-stroke lead over Mike McCullough and David Graham in the $1.3 million tournament.

``I've played poorly all this year, mostly because of my irons,'' Thompson said. ``I've had four lessons in the last month from four different people and they have all helped a lot.''

Thompson said the instructors have included fellow pros and Grant Thomas, a junior college player in Paris, Texas.

``This young man helped me with my pitch shots last week and I pitched one in from the gunk on the 11th hole for a birdie and made three straight birdies after that,'' Thompson said.

Thompson used a sand wedge from about 25 yards out on the 426-yard par-4 11th to start his birdie streak.

``My driving and putting have been good all year, it's my iron play that's given me trouble,'' Thompson said. ``I didn't have any birdie putts longer than 30 feet, and I'm a pretty good putter.''

McCullough, winless in four seasons on the tour, also had a bogey-free round on the Boone Valley course.

``I didn't do anything spectacular, but I got some birdies when I had to,'' McCullough said. ``It was just a good solid round.''

Lee Trevino, Dave Eichelberger, Buddy Allin, Dale Douglass and Bruce Summerhays opened with 68s.

Larry Nelson, making his senior debut, topped a seven-player group at 69. Nelson, who turned 50 on Wednesday, won the 1981 and 1987 PGA Championships and the 1983 U.S. Open. He tied for second in the Doral-Ryder Open in March, and earned $196,981 in 18 PGA Tour starts this year.

Hale Irwin, a Joplin native who lives in St. Louis, was four back after a 70. He leads the tour with six victories and $1,511,989 in 16 starts.

Gibby Gilbert, the 1996 winner, was disqualified for failing to sign his scorecard after shooting an 83.