Selected by the Buffalo Sabres with No. 8 pick in the 2013 NHL Draft following his second season with his hometown team (TPS Turku) in Liiga, Finland's top professional league, Rasmus Ristolainen wasted no time making the NHL.
Immediately coming over to North America, Ristolainen made the Sabres out of training camp and made his NHL debut as an 18-year-old defenseman against the Detroit Red Wings on Oct. 2, 2013. He recorded his first NHL point, a goal, later that month in a 3-1 win against the Florida Panthers on Oct. 25, but he ultimately split the season between Buffalo and Rochester of the American Hockey League. In 34 NHL games, he had two goals and two assists.