Williams staved off elimination by winning the 14th hole, but Chestnut took the next with a birdie 4 to close out the match. Chestnut also topped Derek Berg 4-and-3 in a morning match.
I have been playing pretty good, said the third-year Universtity of Michigan State law student.
Two rounds of match play Tuesday at the Milwaukee Country Club trimmed the field to eight going into Wednesdays quarterfinal and semifinal matches. A 36-hole finale Thursday will decide the championship.
Tim Mickelson and Jordan Byrd, college golf coaches who are both brothers of prominent members of the PGA TOUR, were eliminated in the morning round.
The 26-year-old Chestnut played professionally for one year on the Hooters Tour after graduating from Michigan State in 2005. He entered law school after not succeeding as a pro and regained his amateur status in 2007. He was one of 12 former pros in the third round field of 16 who are now amateurs.
I kind of missed amateur golf. Its just more fun. If you dont play well its not what you do for a living, you get over it, said Chestnut, who will graduate next year.
The other golfers advancing to the quarterfinals are Sean Knapp, Todd Mitchell, Steven Wilson, Jeffrey Wilson, Michael Stamberger, Michael McCoy, and Chris Lange.
Mickelson, the University of San Diego coach and younger brother of Phil Mickelson, lost to Stamberger 1-up.
I just played awful, said Mickelson. I didnt drive the ball very well. I probably missed six fairways, which for me is a lot, and I hit a couple poor iron shots.
Stamberger said his victory did not mean more because of his opponents last name. However, he admitted I guess for people back at home its probably a big deal.
Byrd, whose brother Jonathan caddied for him, lost to Steve White in 23 holes. White squared the match with a birdie 3 on the 16th hole and won with a par 4 on the fifth extra hole.
The Clemson University coach said he did not play well but loved having his brother carry his bag.
It worked out great. We had a good time together, Jordan said.
But after the round when a Golf Channel reporter interviewed Jonathan first, Jordan could be heard saying softly Hes stealing the spotlight again, gol-dang.
After playing Sunday in the BMW Championship, Byrd caddied for his brother Monday and Tuesday.
It was a good experience. I enjoyed watching my brother play and seeing him compete, he said. I was very proud of him.