The California native pitched for the Wild Things during a brief stint in 2013. The southpaw appeared in eight games for Washington and allowed four earned runs and six hits in 7 2/3 innings.

Following the 2013 season, Messner signed a contract with the San Francisco Giants organization. Shortly thereafter, the Giants assigned him to pitch for their Class-A team-the Augusta Greenjackets. 

With the Greenjackets in 2014, Messner went 7-5 and had a 4.17 ERA in 31 games. He started in 12 games and worked 110 innings. Messner surrendered 139 hits, struck out 82 of his opponents, and registered a 2.10 strikeout-to-walk ratio.

Collegiately, Messner pitched for two NAIA schools, Cal State San Marcos and Oklahoma Baptist University. In one season at Cal State San Marcos, Messner had a 7-3 record in 15 games (13 starts) with a 2.91 ERA in 80 1/3 innings. Additionally, Messner became the fourth pitcher in program history to record double-digit strikeouts in a game, when he retired 10 batters on April 13, 2013. Messner recorded a .199 OBA, making him the fourth lowest single-season opposing average in Cal State history. Prior to Cal State, Messner pitched at Oklahoma Baptist where he posted an 8-4 record with a 2.82 ERA in 83 innings.