Zadorov scored on 5-on-3 advantages in a 1:01 span in the second period to give Russia a 4-3 lead. The 6-foot-4 defenseman plays for the London Knights in the Ontario Hockey League.
Pavel Buchnevich also scored twice for Russia, Mikhail Grigorenko added a goal, and Andrei Vasilevski made 30 saves.
New Jersey Devils farmhand Stefan Matteau, Plymouth Whalers forward Ryan Hartman and Wisconsin's Nic Kerdiles had first-period goals for the United States, the tournament winner last year in Russia. Providence's John Gillies stopped 20 shots.
Russia faces the Sweden-Slovakia winner in the semifinals. In the other quarterfinals, Canada faced Switzerland, and the Czech Republic played Finland.
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