The use of communication signal echoes for monostatic radar sensing is an emerging research area in the field of joint radar and communication (JRC). Block orthogonal frequency division multiplexing (OFDM) modulation with cyclic prefix (CP) is widely adopted by many wireless communication standards in the mm-wave band, such as IEEE 802.11ad and cellular vehicle-to-vehicle sidelink in the Frequency Range 2 band. The echoes/reflections of such transmissions may be exploited as a signal-of-opportunity for JRC. However, the cyclostationary property of the CP in block-OFDM signals gives rise to high side-lobes in the radar sensing output. The communication preamble also tends to yield high side-lobes at non-zero Doppler values. To address these challenges, we propose to use zero-prefix OFDM (ZP-OFDM) instead of CP-OFDM as the radar reference in the monostatic radar receiver, perform separate radar sensing on the preamble and data payload parts of the communication echo signal, then combine the separate sensing outputs using a novel radar fusion method, i.e., point-wise minimum selection (min-point selection (MPS) in short). Both analytical and simulation results of Doppler resolution, average/peak side-lobe level, and correct-delay–Doppler-bin detection rate (i.e., the detection rate evaluated at the delay–Doppler bin of the true target response) show that significant radar sensing performance improvement can be obtained by using the proposed method (ZP-OFDM-MPS).