2009-10: Sinitsyn played for the Dallas Stars U16 midget team after moving to America from his native Russia to attend high school. In 57 games with the Stars he scored 24 goals with 28 assists and had 44 penalty minutes.
2010-11: Sinitsyn was the leading scorer for the Dallas Stars U16 midget team from his defenseman position – scoring 11 goals with 20 assists in 36 games. He was drafted by the Green Bay Gamblers in the 5th round (74th overall) of the USHL Entry Draft and drafted by Barys Astana in the second round (38th overall) of the 2011 KHL Draft.
2011-12: Originally intending to play in the USHL, Sinitsyn was forced to return to Russia when his student visa expired. He played seven games for Zelenograd in the Russian Minor Hockey League's B division while in Russia and was scoreless and plus-two with 10 penalty minutes. He returned to North America in December and enrolled at the University of Massachusetts-Lowell. Sinitsyn practiced with the Red Hawks but did not appear in any games – maintaining all four years of his NCAA eligibility. Not among the 210 players in Central Scouting's final rankings prior to the 2012 NHL Draft, he was selected by Dallas in the seventh round (183rd overall).
From U-16 Dallas Stars Head Coach and USNTDP Scout Eric Silverman: A player that would have gone way higher if it weren’t for visa issues, Sinitsyn is an offensive defenseman with a great skillset. “First round tools” with size, skating and shooting. He moves the puck well and had a pro-level shot before even being draft-eligible. Has a lethal one-timer and is especially effective on the power play. Makes a good first pass and is more of a passer than a puck-rusher. “[As good or better] offensive tools as the top U.S. players in the  Draft.” A tough player that can give or take physicality if he needs to, still a little more of a retaliatory vigilante than his coaches will like. Tries to make the perfect or fancy play too often, doesn’t like the simple play and isn’t very content to just get the puck out of the zone without it turning into an offensive counter-attack. Needs to improve his sense and work rate still and mature as a player overall. Very good kid off the ice that speaks three languages and is prepared to take on any challenges.
Was redshirted before he could become the youngest D1 hockey player in the country, but figures to be an impactful player at UMass-Lowell in 2012-13.