On the first day of the 2018 Summer Youth Olympics in Buenos Aires, Argentina, Markov won his first gold medal in the 4×100 metre mixed freestyle relay for his efforts in the prelims heats, where he swam a 50.28 for the lead-off leg of the relay to qualify the relay to the final ranked eighth. For his next event, the 100 metre butterfly, Markov swam a personal best time of 53.91 seconds in the prelims heats before placing 13th overall in the semifinals with a time of 54.07 seconds.Omega Timing; Atos (12 October 2018). "Buenos Aires 2018 Youth Olympic Games: Official Results Book Swimming". International Olympic Committee. Retrieved 2 December 2021. Day three of competition, Markov ranked first in the semifinals of the 50 metre freestyle with a time of 22.30 seconds and qualified for the final.Sutherland, James (9 October 2018). "2018 Youth Olympic Games: Day 3 Finals Live Recap". SwimSwam. Retrieved 2 December 2021. Following his semifinals performance, Markov won a gold medal in the 4×100 metre freestyle relay with finals relay members Kliment Kolesnikov, Vladislav Gerasimenko, and Andrei Minakov in a time of 3:18.11.Pimer, Diana (9 October 2018). "2018 Youth Olympic Games Night Three Recap: Andrei Minakov Climbs World Ranks". Swimming World. Retrieved 2 December 2021."Eastern European swimmers rule in the pool". Olympics.com. 9 October 2018. Retrieved 2 December 2021. On day four, Markov won his first individual medal of the Youth Olympic Games in the 50 metre freestyle, placing second and winning the silver medal in a time of 22.37 seconds, which was just 0.04 seconds slower than gold medalist Thomas Ceccon of Italy.Sutherland, James (10 October 2018). "2018 Youth Olympic Games: Day 4 Finals Live Recap". SwimSwam. Retrieved 2 December 2021.Pimer, Diana (10 October 2018). "Youth Olympic Games Night Four Recap: Russia Takes Down 4 x 100 Medley Relay World Junior Record". SwimSwam. Retrieved 2 December 2021. Later in the day, Markov won a gold medal and set a world junior record in the 4×100 metre medley relay at 3:35.17, splitting a 49.19 for the freestyle leg of the relay.Sutherland, James (10 October 2018). "Kolesnikov, Minakov Lift Russians To New WJR In 400 Medley Relay". SwimSwam. Retrieved 2 December 2021."Russia's swimmers come good again". Olympics.com. 10 October 2018. Retrieved 2 December 2021.
