Abstract: Natural rock masses inevitably contain inherent flaws, which exert a significant impact on the mechanical properties, on the failure behaviors of rock masses and, on the rock-breaking performance of tunnel boring machine (TBM) disc cutters. The combined finite-discrete element method (FDEM) was adopted to investigate the effects of pre-existing oval hole characteristics—including quantity, inclination angle, and azimuth angle—on the mechanical properties and failure behaviors of specimens under uniaxial compression and direct tension. Furthermore, the influence of such pre-existing holes on the rock-breaking efficiency of single and double TBM disc cutters was assessed. The research results obtain following conclusions: With an increase in the inclination angle of pre-existing holes, compressive strength rises exponentially and elastic modulus grows in an S-shaped pattern, while the azimuth angle has a negligible influence. Conversely, the tensile strength of specimens increases in an S-shaped curve as both the inclination and azimuth angles of pre-existing holes increase. The impact of pre-existing holes on TBM disc cutter rock-breaking efficiency is determined by their relative positions. For single disc cutter operation, an appropriate double-hole spacing (l_2h=8 cm~14 cm) enhances rock-breaking performance—marked by increased debris volume, reduced specific energy, and improved efficiency—whereas an overly small spacing (l_2h≤6 cm) inhibits rock breaking by suppressing lateral crack propagation. In double disc cutter rock breaking, with a fixed cutter spacing (e.g., d_c=13 cm), pre-existing holes between adjacent cutters can enhance rock-breaking efficiency. Specifically, at l_2h≤10 cm, this effect translates to a lower cutter thrust and smaller rock debris size. Conversely, holes positioned below, adjacent to, or outside the area of adjacent cutters (e.g., 12 cm≤l_2h≤22 cm) inhibit rock breaking, leading to the formation of unbroken rock ridges between cutters. In contrast to intact rock specimens, the TBM disc cutter spacing needs to be reduced for rock masses rich in pre-existing holes, thereby preventing the formation of unbroken rock ridges between adjacent cutters.