In 1918–19, Foyston scored 15 goals in 18 regular season games, and three goals in two playoff games, as Seattle advanced to the 1919 Stanley Cup Finals against the Canadiens. Foyston scored nine goals in five games before the series was abandoned (with the teams tied at 2-2 in a best-of-five series format) due to the influenza epidemic. The Stanley Cup was not awarded that year. The following season, in 1919–20, Foyston scored 26 goals in 22 regular season games, and three goals in two playoff games, as Seattle advanced to the 1920 Stanley Cup Finals. In the Finals, he had six goals in five games.