2009-10: Alex Sakellaropoulos played for the Chicago Fury U16 team in Illinois. In 24 games he had a 3.04 save percentage. He was selected by Sioux Falls in the sixth round (88th overall) of the 2010 USHL Futures Draft and was chosen by Niagara in the ninth round (167th overall) of the 2010 OHL Priority Draft.
2010-11: Sakellaropoulos skated for the Fury's U18 team. In 28 games he had a 2.77 goals against and .892 save percentage.
2011-12: Sakellaropoulos played 25 games for the Chicago Steel in his first USHL season. As a backup to 20-year-old goalie Mathias Dahlstrom from Sweden, he was 8-10-1 with a 3.28 goals against and .903 save percentage.
2012-13: Sakellaropoulos started 44 of 64 games for the Chicago Steel in his second USHL season — setting a team record for wins (20). He was 22-20-2 with three shutouts and had a 3.03 goals against and .914 save percentage. Chicago finished fifth in the Eastern Division; missing the USHL playoffs. Sakellaropoulos played in the USHL/NHL Top Prospects Game in January 2013, stopping all nine shots he faced, and in April he committed to playing at Union College in 2013-14.
2013-14: Sakellaropoulos appeared in eight games as a backup to junior Colin Stevens in his freshman season at Union College. He was 4-2-2 with one shutout and had a 2.02 goals against and .927 save percentage. Sakellaropoulos was not among the 34 North American goalies in Central Scouting's mid-term rankings prior to the 2014 NHL Draft.