Detect-and-Forward (DF) is a cooperative technique based on the retransmission of a detected version of the transmit signal. It improves performance, throughput and cellular coverage. However, in cellular scenarios, it coexists with co-channel interference (CCI), which is the principal factor that affects the performance of cellular networks. On the other hand, Optimum Combining (OC) is a low complexity combining technique that maximizes the signal-to-interference-plus-noise ratio (SINR), achieving in this case diversity gain by eliminating the CCI. In the present paper, the performance of cooperative DF network in the presence of multiple CCI at relay and destination is analysed, where relay and destination are equipped with multiple antennas and OC. Furthermore, scenarios by considering multiple antenna transmission (MAT) and transmit antenna selection (TAS) technique at relay are supposed. For both MAT and TAS techniques, a tight approximation of the end-to-end instantaneous SINR is proposed. Subsequently, its moment-generating function is derived in closed-form in order to evaluate the average bit-error rate of the system. Analytical results are validated using Monte-Carlo simulations for several scenarios, showing that OC eliminates fully the CCI, even in the case of high-power CCI. The diversity gain depends on the number of destination antennas, relay antennas and interferers.