[1][2] Ristolainen made his NHL debut with the Buffalo Sabres on the opening night of the 2013–14 season, on 2 October 2013, against the Detroit Red Wings.

[4] In doing so, he became the first Sabres' defenceman to score a hat-trick since Hockey Hall of Famer Phil Housley did so in the 1987–88 season.

[5] On 21 March 2017, Ristolainen delivered a check to Pittsburgh Penguins forward Jake Guentzel.

Guentzel suffered a concussion on the play, and Ristolainen was given a three-game suspension for interference by the league.

[8] On 5 January 2014, Ristolainen scored the overtime winner in the final of the 2014 World Junior Ice Hockey Championships against previously undefeated Sweden, giving Finland the gold medal.