The event of 8 September 2017 was characterized by the effects of the arrival of two interplanetary coronal mass ejections on September 6^th and 7^th and a resultant geomagnetic storm. This storm event has been widely studied due to its extreme geo-effectiveness in the global geospace. In the inner magnetosphere, the effects included a distinct intensification of the ring current and a severely eroded plasmasphere. However, little attention has been paid to the role that the observed substorm injections played on the storm-time ring current. Starting at 1209 UT on September 8^th, multiple substorm onsets occurred spreading over a wide magnetic local time range on the dawn side. Multiple substorm injections were observed simultaneously at geosynchronous orbit by the Los Alamos National Laboratory satellites and the Geostationary Operational Environmental Satellites, and by both the Exploration of energization and Radiation in Geospace/Arase and the Van Allen Probes missions deep in the inner magnetosphere. Subsequent buildup of the ring current was observed. In this study, we will investigate the role of the substorm injections on the extreme ring current response by numerical simulations with the physics-based Comprehensive Inner Magnetosphere-Ionosphere model using the geosynchronous data as boundary conditions to the model. Since the ring current has a strong influence on the inner magnetospheric dynamics, we also consider its impacts on the dynamics of the electric field and the plasmasphere. Furthermore, this study addresses the critical need to include substorms in evaluating the geo-effectiveness of geomagnetic storms.