The initiation of the caving process in block/panel caving is critical to the success of mines. However, there is no widely adopted methodology for modeling the onset of caving. This study proposes a methodology to model the initial stages of caving using the Discrete Element Method, in which the rock mass is represented using the Bonded Particle Model, and the undercut material is modeled with non-cohesive discrete particles. The collapse of the rock mass was replicated following a parameter calibration process, and the results were compared with actual mining data of the observed initial fragmentation. Key parameters were identified, such as allowable normal and shear stresses, which are essential to accurately represent the collapse of the rock mass and the evolution of the early stage of rock fragmentation. Low allowable stress values led to premature collapse and finer fragmentation, whereas higher values delayed cave back failure and resulted in coarser initial fragmentation. The results showed the formation of large rock fragments between 14 and 15 m during the initial cave back failures. Subsequently, larger fragments ranging from 2 to 9 m were observed detaching from the cave back as draw progressed, with sizes comparable to those reported in some block/panel caving operations. The main contribution of this work is a methodology that demonstrates the feasibility of modeling caving initiation, which is crucial in a context where increasing rock mass strength and deposit depth require design changes at the production level and pose significant uncertainty in the rock mass response.