In
AJGA events, Koivun lost a playoff in 2021 and won the 2022
Rolex Tournament of Champions. He won the 2022
Junior Presidents Cup with the U.S. national team. He enrolled at
Auburn University and started playing with the
Auburn Tigers men's golf team, where he as a freshman in 2024 recorded one of the best seasons in collegiate golf history. He won the SEC Championship by six shots and only finished outside the top-six once in 13 starts, and had the lowest adjusted scoring average (67.3) in the NCAA. He finished in a tie for second at the
2024 NCAA Division I Men's Individual Championship, and led the Auburn team to win the national title, the first in program history. He was 7–0 in matchplay over the season, leading Auburn to 10 tournament victories, and was named
Southeastern Conference Freshman of the Year and Player of the Year. He became the first player to win all four major collegiate awards, the
Haskins Award, Jack Nicklaus Award,
Ben Hogan Award and Phil Mickelson Award, in the same season. Following his freshman season with Auburn University, Koivun was the third-ranked player in the
World Amateur Golf Ranking, behind
Gordon Sargent, and
Christo Lamprecht. In February 2026, Koivun won the Amer Ari Invitational with rounds of 62, 62 and 67 for a 25-under par score. Koivun broke Auburn's 54-hole scoring record by seven strokes and his back-to-back 62s (−10) on Thursday and Friday, broke the NCAA 36-hole record of 18 shots under par, previously set by
Tiger Woods at the 1996 Pac-10 Championship. He was also the first player in NCAA history to post two rounds of 62 or lower in the same event. One week later, Koivun won the Gator Invitational for his seventh career college victory, the most of any golfer in Auburn's history. In March, Koivun won The Hayt for his third win in four starts. In April, Koivun won the Mason Rudolph Championship, the Ford Collegiate, and the SEC Championship for the third straight year. Koivun became just the second golfer to win three straight SEC titles, joining LSU's
Mac McLendon, who accomplished the feat from 1965-67. Koivun finished at 19-under 191, an SEC scoring record and tying himself from earlier in 2026 at the Amer Ari Invitational for the third-lowest total score in college golf history. ==Amateur wins==