In this paper, we present a novel contention based cross-layer synchronous MAC protocol, CROP-MAC, to reduce the end-to-end transmission delay and energy consumption by optimizing the pipelined flow of data packets in wireless sensor networks. CROP-MAC optimizes pipelined flow with the help of staggered sleep/wake scheduling, efficient synchronization and appropriate use of routing layer information. Staggered sleep/wake scheduling and routing layer information enable CROP-MAC to schedule source to sink transmission of multiple data packets in a single cycle. We evaluate CROP-MAC through ns-2.35 simulations and compare it with PMAC, PRMAC and BulkMAC. Simulation results show, CROP-MAC outperforms best of the three protocols by 608.89 %, 14.36 % and 12.5 % in terms of end-to-end transmission delay, packet delivery ratio and energy consumption, respectively.