Decentralized signal control of congested traffic networks based on the Max-Pressure (MP) controller is theoretically proven to maximize throughput, stabilize the system and balance queues for single intersections under specific conditions. However, its performance for wide implementation requires further attention. Increased implementation cost related to queue monitoring in controlled intersections reduces MP applicability. Aiming at reducing this cost, we propose a strategy for identifying the most critical network intersections to introduce MP control, with the aim of reaching high efficiency without a full-network implementation. The proposed selection process is based on node congestion and queue variance data. A modified version of Store-and-Forward dynamic traffic model is used to emulate spatio-temporal traffic evolution in a large-scale network with more than 500 intersections and evaluate system performance for different MP node layouts. Results show that more than 90% of the improvement observed when all network nodes are controlled can be achieved by controlling only 20% of nodes, selected via the proposed strategy, thus significantly reducing implementation cost. The impact of MP application in network traffic characteristics is demonstrated through detailed analysis.