The 2021 Lamar Hunt U.S. Open Cup tournament proper was to feature teams from all five tiers of the men's American soccer pyramid.
The tournament itself was downsized to 16 teams, before ultimately being canceled for the second consecutive season due to the pandemic.
The NISA Fall Champion, Detroit City FC, retroactively qualified on October 2, 2020.
Bold = winner* = after extra time, ( ) = penalty shootout scoreSource: nisaofficial.com The 2020 USL League One champion, Greenville Triumph SC qualified.
Greenville was awarded the title based on points per game average (2.188 to 1.825), and reached the Open Cup.