Mills earned an invitation to the 2012 Masters Tournament with the victory.
The 21-year-old Mills, from Easley, S.C., is the first qualifying medalist to win the title since former Clemson star D.J. Trahan in 2000. He squared the match with a conceded eagle on the 35th hole and matched Ernst with a par on the 36th to force the extra hole on Bandon Dunes' Old Macdonald course.
The tournament is limited to players who don't hold privileges at any course that doesn't extend playing privileges to the general public.
Mills joins Kevin Johnson (1987) and Trahan as former Clemson players to have won this tournament.
- Also at Bandon Dunes, UCLA's Brianna Do won the Women's U.S. Amateur Public Links, beating Texas high school star Marissa Dodd 1-up.
The 21-year-old Do was born in California but represented her parents' home country of Vietnam this week.
CHAMPIONS TOUR: In Blainville, Quebec, Taiwan's Lu Chien-soon shot 9-under-par 63 to match the course record and take a one-stroke lead over John Cook after the second round of the Champions Tour's Montreal Championship.
Lu bogeyed the opening hole, then had 10 birdies in a 13-hole stretch from Nos. 5 to 17 to reach 16-under at Fontainebleau Golf Club. He tied the course record set last year by D.A. Weibring in the inaugural tournament and matched Friday by Cook and John Huston.
The 51-year-old player has fought a debilitating back injury. Having previously attributed part of his recovery to drinking wine, he had a surprising twist to offer when asked about his preparation for Saturday.
"British beer," said Lu, who said he planned to stick with what was working as he got ready to face the final round.
"Just a little bit, beer."
Cook, a two-time winner this year, had 66.
Defending champion and Augusta native Larry Mize had 69 and is tied for 12th place, six shots off the lead at 128.
Former Augustan Allen Doyle had 72 and is tied for 64th place at 141.
EUROPEAN TOUR: In Saint-Quentin-En Yvelines, France, Mark Foster shot 3-under-par 68 to share the lead with James Morrison after the third round at the French Open.
Foster made up for two bogeys with five birdies for a 9-under total of 204. Morrison shot 72.
Richie Ramsay (69) is in third place, one shot back.
- In Bara, Sweden, former Augusta State golfer James Heath shot 3-under-par 69 and is seven shots off the clubhouse lead in the Challenge Tour's Princess by Schuco.
Andrea Harto had 63 and is the leader at 12-under 264 in the weather-delayed tournament. The players who didn't complete the third round Saturday will do so this morning, with the final round to follow.