The Czechs led 3-1 in the first period, but Canada came back to tie the score twice at 3-3 and 4-4 in the last two sessions.
Sidney Crosby, one of the NHL's top rookies this season with the Pittsburgh Penguins, scored Canada's last goal 1:01 into the third to make it 4-4 after beating goalie Milan Hnilicka with a backhander off his own rebound.
It was Crosby's sixth goal, the most in the tournament.
Five minutes later, Balastik put the Czechs ahead for good, scoring with a slap shot from virtually an impossible angle near the boards in the Canadian end.
Alex Auld gave up another goal at 13:39 as Martin Erat beat the Canadian goalie with a one-timer off David Vyborny's pass after a quick Czech 2-on-1 break.
"We started very good when we scored two early goals and fought well when they came back in the last two periods," Czech Republic coach Alois Hadamczik said.
Atlanta Thrashers forward Marian Hossa, who missed Slovakia's last two games with a knee injury, set the tone for Slovakia, scoring 1:45 into the game.
Martin Cibak, Rene Vydareny, Marcel Hossa and Andrej Kollar also scored for Slovakia, which never trailed in the game.
Slovakia coach Frantisek Hossa said Marian Hossa's return gave his teammates a big boost, and several agreed.
"Marian is the best player on our team and we need him very much and it's unbelievable ... that he gets hurt like that and came back to play for Slovakia," Cibak said. "That's a big help for us, and mentally and physically we were ready tonight and I think we played better hockey than Sweden."
Magnus Johansson and Andreas Karlsson scored second-period goals for Sweden, which entered the game with an unbeaten record but played listlessly at times.
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