Alamouti Code makes use of a rich algebraic structure to provide diversity gains with small decoding complexity. In this work, we investigate the problem of co-channel interference (CCI) mitigation for two users applying AC in flat fading and quasistatic wireless channels. By exploring the algebraic properties of Alamouti matrix, we develop a selective CCI mitigation method at the receiver. Assuming that zero-forcing (ZF) or minimum mean-squared error (MMSE) interference suppression techniques are used to separate two users and according to post-filtering instantaneous signal-to-noise-ratio (ISNR) or instantaneous signal-to-interference-plus-noise ratio (ISINR), we derive a very simple unified selection formula, avoiding computing the inverse (pseudoinverse) of channel matrix. Through the selection, we detect the user with higher post-filtering ISNR or ISINR, and then subtract its contribution from the received signals and detect another user. The complexity analysis and simulation results show that our method demonstrates better performance versus complexity tradeoff compared to the existing methods.