We present two event studies of significant enhancements of relativistic electron flux in the slot region of Earth's radiation belts during storms, using electron measurements from the Akebono spacecraft at high altitudes and NOAA 15, 16, 17, and 18 at low altitudes. These flux enhancements take place during the main phase of storms, and occur rapidly on timescales of less than 60 min. In association with storm time substorms, the magnetic field at geosynchronous altitude becomes highly stretched, intensifies, and then returns to a more dipolar configuration. The flux enhancements in the slot region are likely associated with these large changes in the nightside magnetic field configuration. The observations imply that rapid particle acceleration and/or transport processes operate in the inner (L < 3) magnetosphere in association with large substorms during the main phase of a storm.