Stevenson shot rounds of 71-66-65 to win. His final round, 6-under 65, was the low round of the tournament of any golfer.
The Florida Gulf Coast University freshman recorded six birdies and no bogeys, including a four-hole birdie stretch from Holes No. 4-7, going on a hot streak to chase down the leaders.
He made par on the next nine holes, entering the par-3 No. 17 at 9-under. Andre Zhu and Kent Hsiao trailed by just one shot at 8-under.
Stevenson went on to birdie No. 17 and the par-5 No. 18 and win by two shots over Zhu, who finished in solo second place at 9-under.
Hsiao, who was the 36-hole leader, finished in solo third place at 8-under. Darren Zhou and Camden Goldknopf finished T4 at 7-under. Goldknopf was the leader after the first round.
Stevenson played the final 32 holes of the tournament 11-under par without a bogey. The Bartram Trail graduate moved from three shots behind leader Hsiao after 36 holes in a rainy final round.
The win continued his recent momentum, as he played in one fall tournament for FGCU, shooting a final-round 67 at the Kapolei Invitational in Hawaii.
“On the back nine when it got a little rainy and it was crunch time, I relied on my short game,” Stevenson told the St. Augustine Amateur staff. “I made quite a few up and downs and par saves to keep the round going. I felt the best I’ve ever felt coming in here. Playing with all the seniors in college helped with my experience.”
The St. Augustine Amateur is a national event established in 2004 for top amateur and collegiate players. The winner receives the John C. Jennison III trophy. The tournament is open to amateurs only whose entry has been accepted by the tournament committee. However, there is an open qualifier.