The payoff was his selection by the Oakland A's in the fifth round of the 2014 draft.
"It was a long road," Fillmyer said shortly after he was selected by the A's on June 6, with the 162d overall pick. "I told myself the day I decided to try this that one day it would work out, and it did."
The 6-foot-1, 190-pound Fillmyer put together a sensational sophomore season for Mercer County. He was 9-0 with a 0.68 ERA and 94 strikeouts in 66 innings.
Mercer County coach Kevin Kerins said Fillmyer was especially intriguing to major-league scouts because of his background.
"They see a fresh arm," Kerins said. "He threw less than 10 innings last year, 66 innings this season. He hardly pitched in high school.
"He doesn't have the wear and tear on his arm that so many other top prospects have."
Kerins said Fillmyer's fastball hit 97 m.p.h. on a radar gun this season and consistently sat in the 92-94-m.p.h. range.
"He just has a tremendous arm," Kerins said.
Fillmyer was a shortstop at Florence, a second-team All-South Jersey selection and a key member of the Burlington County team that won the Carpenter Cup Classic in June 2012.
Fillmyer said he might have pitched 10 innings, total, as a junior and senior at Florence.
"I would close once in a while," Fillmyer said of his experience on the mound.
Florence coach Joe Frappolli Jr. said Fillmyer was a top all-around player for the Flashes.
"His range as a shortstop was incredible," Frappolli said. "He would get balls on the other side of second base. He had great bat speed, too."
Frappolli said Fillmyer served as an occasional closer but wasn't much of a pitcher for the Flashes.
"He had a great arm, but he really wasn't a pitcher for us," Frappolli said. "It's a great story how it worked out, small-town kid who is getting a chance with the pros."
Fillmyer's freshman season at Mercer County was similar to his high school career. He was a shortstop, first and foremost, and made a few relief appearances.
But when the Rockies selected him in the draft and told him they projected him as a pitcher, Fillmyer realized his future was on the mound.
"Once I decided not to sign and come back for another year, I was like, 'That's it. I'm a pitcher now,' " Fillmyer said. "I told myself I could do it. I told myself that as a pitcher I could get myself somewhere in life."
Fillmyer said he planned to sign with the A's. The bonus slot allotment for the 162d pick was $288,300.
"I'm 20. It's time to get going," Fillmyer said.