Harper, sporting a red Canada jersey with his name and No. 1 on the back, watched from about 10 rows back as Canada defeated Russia 5-4 at Air Canada Centre.
"Congratulations to #TeamCanada on their outstanding performance tonight. You've made your country extremely proud. #WJC2015 #BigPlay," Harper said in a tweet shortly after the victory.
The PM is an avid hockey fan and has written a book on the sport's early days.
"You can't beat the atmosphere here," Harper said in an interview on TSN. "You have to be here to believe it. It's just so exciting."
Between periods, Harper walked down to ice level to shake hands and take pictures with fans.
Harper met with Ontario Premier Kathleen Wynne earlier in the evening.
Follow @GregoryStrongCP on Twitter.