2010-11: Zach Bratina played for the Central Ontario Wolves bantam team near his hometown of Lindsay.
2011-12: Bratina appeared in five games with the junior A Lindsay Muskies as a 16-year old and was one of the top forwards on the Central Ontario Wolves midget minor AAA team. He scored 2 goals and had 2 penalty minutes in OJHL play with the Muskies. Bratina scored 22 goals with 21 assists and had 60 penalty minutes in 30 games for the Wolves. Bratina was selected by Plymouth in the first round (19th overall) of the 2012 OHL Priority Draft.
2012-13: Bratina began his rookie OHL season with Plymouth before being traded to Saginaw as part of the package sent to the Spirit to obtain 19-year-old Vince Trocheck (FLA). Bratina scored 4 goals with 4 assists and was +1 with 16 penalty minutes in 37 games for the Whalers. Injuries limited Bratina to 13 regular season games with the Spirit. He scored 2 goals with 4 assists and was +3 with 11 penalty minutes. Saginaw finished fourth in the West Division and was swept by eventual OHL champion London in a first round playoff series. Bratina had 1 assist and was -2 with 6 penalty minutes in three playoff games.
2013-14: Bratina skated in 30 games for Saginaw before being involved in another mid-season trade — going from the Spirit to North Bay in exchange for 2013 All-Rookie second team selection Blake Clarke. The trade to the Central Division first-place Battalion worked well for Bratina. The 18-year-old scored 5 goals with 9 assists and was +1 with 48 penalty minutes playing for the Spirit. In 28 games with North Bay he was +7 with 7 goals, 9 assists and 27 penalty minutes.