2009-10: Prokhorkin played for the Podolsk Vityaz junior team in Russia. In 54 games he scored 52 goals with 74 assists and had 60 penalty minutes. Vityaz finished second in the Moscow Region. In seven qualifying games he scored 5 goals with 10 assists and had 12 penalty minutes as Vityaz finished second in the six-team tournament. Prokhorkin was selected by Vityaz Chekhov in the second round (26th overall) of the KHL Draft.
2010-11: Obtained by CSKA Moscow in the summer, Prokhorkin made his KHL debut, skating in six games with CSKA Moscow, and was the fourth-leading goal scorer for the MHL-champion CSKA-Red Army junior team. He was scoreless and minus-three in limited ice time in the KHL. Prokhorkin scored 23 goals with 17 assists and was plus-28 with 42 penalty minutes in 46 games for the junior team. In 16 MHL playoff games he scored 3 goals with 5 assists and was plus-seven with 10 penalty minutes. CSKA-Red Army defeated Magnitogorsk in the MHL finals.
2011-12: Prokhorkin battled injuries in his second season in Moscow – appearing in 15 regular season games and four playoff contests for CSKA Moscow in the KHL and skating for CSKA Moscow-Red Army's MHL squad. He scored his first KHL goal and was minus-one with 1 assist and 4 penalty minutes while averaging eight minutes of ice time for CSKA. In the KHL playoffs he had 1 assist and was plus-one with 2 penalty minutes. Prokhorkin scored 9 goals with 17 assists and was plus-13 with 47 penalty minutes in 15 games for CSKA Moscow-Red Army in MHL play. He scored 2 goals with 9 assists and was plus-one in 16 playoff games as CSKA-Red Army reached the MHL finals; falling to Omskie Yastreby. Prokhorkin was invited to the 2012 NHL Draft Combine and was ranked ninth amongst European skaters in Central Scouting's final rankings prior to the 2012 NHL Draft.