The purpose of this study was to identify the external demands during official under-18 basketball matches that included four quarters (Q1, Q2, Q3, Q4) and/or overtime (OT) periods. Variables included: 1) distance covered and distance covered within four intensity zones (standing-walking S-W, jogging JOG, running RUN, and high-speed running HSR); 2) explosive efforts per minute (EEs); 3) PlayerLoad (PL); 4) the number of jumps per minute; 5) the number of accelerations above 2 m∙s2 (ACCs); and 6) the number of decelerations above −2 m∙s2 per minute (DECs). The values for total distance, JOG, RUN, HSR, PL, ACC, and DEC were significantly smaller during periods Q2, Q3, Q4, and OT compared to Q1. In addition, the number of EEs during Q1 was significantly greater than during Q3, Q4, and OT. When comparing OT periods to Q2, there were significantly smaller values for total distance, RUN, and PL. Similarly, when comparing OT periods to Q3, significantly smaller values were found for PL. Furthermore, when comparing OT periods to Q4, significantly smaller values were achieved for total distance and PL. These findings indicate that players experienced a decrease in external physical demands as the match progressed to an OT period. This decrease may be indicative of player fatigue and/or strategic changes that should be considered by practitioners in the preparation and management of players for overall team success in junior basketball competitions.