Kammala jumla mai zuwa: Ristolainen ya fara buga wasan NHL tare da Buffalo Sabres a daren farko na kakar 2013-14, a ranar 2 ga Oktoba, 2013, a kan Detroit Red Wings. Ya zira kwallaye na farko na NHL a cikin watan, a ranar 25 ga Oktoba a kan Jacob Markström na Florida Panthers. A ranar 5 ga Janairu, 2014, Ristolainen ya zira kwallaye a wasan karshe na gasar.
2014 Gasar Hockey ta Duniya ta Junior Ice da Sweden da ba a ci nasara ba a baya, ta ba Finland lambar zinare. Ya zira kwallaye na farko na NHL a ranar 10 ga Disamba 2015 a kan Calgary Flames. A yin haka, ya zama dan wasan Sabres na farko da ya zira kwallaye uku tun lokacin da Hockey Hall of Famer Phil Housley ya yi hakan a kakar 1987/88.