'I've been playing golf for so long, and it's probably one of the longest I've ever had,' said Thompson, who posted a five-under 67 for a 36-hole total of eight-under-par 136.
The 45-year-old Thompson, the head professional at Whispering Pines Golf Club in Trinity, Texas, had a little help on the enormous, left-to-right curling putt from his wife, Kris, who is caddying for him this week.
'She said to me, 'I can't read this,'' said Thompson, whose round also included five birdies and two bogeys. 'I was just trying to knock it up there somewhere close from down there to get it up to the hole.'
Thompson, playing in his sixth Club Pro Championship, took a slim one-shot lead into the weekend in steamy Kentucky. Mike Gilmore, the head pro at Wheatley Hills Golf Club in East Williston, New York, shot a five-birdie, one- bogey 68 to finish alone in second place at seven-under 137.
'I got off to a real good start and I'm looking forward to the next two days,' said Gilmore, 37, who nearly holed a 40-foot birdie at Valhalla's 535-yard, par-five finishing hole.
Don Berry of Brooklyn Park, Minnesota, matched Thompson for the day's best round of 67. He led a foursome in third place at four-under 140 that included Tag Wylie (69) of Durham, North Carolina; Barry Evans (70) of Charleston, West Virginia; and Kim Thompson (70) of American Fork, Utah.
Defending champion Wayne DeFrancesco of Baltimore, Maryland, rebounded from a two-over 74 in round one with a four-under 68 on Friday. He pulled within six shots of the top spot and was alongside first-round leader Sean Farren of Oakmont, Pennsylvania; Joseph Klinchock of Pittsburgh, Pennsylvania; and Tim Thelen of Richmond, Texas.
Thelen, the winner of the 2000 CPC at Oak Tree and runner-up to DeFrancesco last year at the Sunriver Resort, also earned the PGA Club Professional Player of the Year Award in 2001.
A total of 84 players from the field of 156 made the cut, which fell at seven- over-par 151.
Among those on the outside looking in was Suzy Whaley of Farmington, Connecticut, the first woman to compete in the CPC.
Although she opened with an eight-over 80 on Thursday, Whaley was still on the good side of the cut after going two-under through 11 holes Friday. But she bogeyed the 12th and 15th holes, then suffered a quadruple-bogey at the par- four 16th en route to a 76 and a 156 total.
The low 25 scorers after 72 holes earn a berth in the 84th PGA Championship, to be held August 15-18 at Hazeltine National Golf Club in Chaska, Minnesota.
In addition, the low nine scorers and 2001 champ DeFrancesco will form the U.S. PGA Cup Team that will take on the Great Britain/Ireland squad in the 21st PGA Cup Matches, February 28 to March 2, 2003, at PGA Golf Club in Port St. Lucie, Florida.
Full field scores from the PGA Club Pro Championship