The 1920–21 National Challenge Cup was the annual open cup held by the United States Football Association now known as the Lamar Hunt U.S. Open Cup.

On September 25, 1920, the National Challenge Cup held a drawing for the first round of the 1921 National Challenge Cup. The drawing paired eighty-five entrants, down from 99 the previous year being due to the fact the entrance fee had been raised from $5 to $10.^[1] The cup a single elimination format consisting of six rounds and a single game final. The entrants were dividing into an eastern and a western division which led to a final pitting St. Louis Scullin Steel F.C. from the west and Brooklyn Robins Dry Dock from the east.

Byes: Maple Leaf F.C.; Gray & Davis F.C.

Byes: Young Thornton F.C.; Potter & Johnson F.C.; Colonial F.C.; Greystone F.C.; Fairlawn Rovers

Byes: Stamford F.C.; Ansonia F.C.; Columbia Gramophone Co.

Byes: Clan MacDuff F.C.; Brooklyn F.C.; Robins Dry Dock F.C.

Byes: Cedar Cliff F.C.

Byes: I.F.L. F.C.; One and All F.C.; Walkerville F.C.; Magyar A.A.F.C.; Caledonia F.C.; Roses F.C.; Ulster F.C.

Byes: Cleveland Greyhounds F.C.; White Motor Co. F.C.; Goodyear F.C.

Byes: Oneida Community Co. F.C.; McNaughton Rangers F.C.; Rochester City Moose F.C.; Rochester Celtic F.C.; Camera Works F.C.; Kodak Park F.C.

Bye: Madison F.C.

Byes: Ben Miller F.C.; St. Louis Screw F.C.; Scullin Steel F.C.; Innisfail F.C.

Bye: Simco F.C.

Byes: Thistles F.C.; Bricklayers F.C.; Harvey F.C.; Swedish American A.A.; Pullman F.C.; Rangers A.C.; Norwegian American A.A.

Home teams listed on top of bracket

(*): replay after tied match
w/o: walkover/forfeit victory awarded

April 19, 1921

Robins Dry Dock (NY)	4–2	Scullin Steel (MO)
McGuire 16' Hosie 29' (Ratican) Sweeney 64' McKelvey (Sweeney)	Report[2]	Bechtold 15' (Nolan), 19'

Fall River, Massachusetts

Attendance: 8,000

Referee: James E. Schofield, Bristol, Connecticut (USA)

• USOpenCup.com