Germany took second place in Group B after a 2-1 win over Italy, and Sweden ended the group stage unbeaten with a 4-0 win over Japan.
The top-ranked Americans are hungry for revenge after losing to Canada in the gold-medal game four years ago and sent a message with a lop-sided drubbing that few expected from the typically well-matched powerhouse teams at Santagiulia Arena.
The win saw the United States clinch the top spot in Group A. Canada, which had never before been shut out in women's Olympic play, have more work to do before the knockouts with a game against Finland on Thursday, and are currently second on six points.
Forward Hannah Bilka scored twice while forward Kirsten Simms and defenders Caroline Harvey and Laila Edwards added goals, as Canada were suffering without their long-time leader Marie-Philip Poulin, who was injured on Monday.
The game at Santagiulia was widely expected to be a preview of the championship, with the United States and Canada the only two nations to top the podium since the event joined the Olympic programme in 1998.
The USA will play hosts Italy in the last eight.
Finland notch first win
Following a scoreless first period, Finland took the lead, converting on the first power play of the game as Viivi Vainikka scored her side's first goal of the Games early in the second period and Julia Liikala made it 2-0 just over six minutes later.
Switzerland scored a shorthanded goal three minutes before the end of the second period, Alina Muller taking the puck all the way from the neutral zone to the net.
Finland responded immediately while still on the power play through Sanni Vanhanen to make it 3-1, which proved to be the final score.
The result means Switzerland finish bottom of the group with two points, with Finland fourth on three points. Finland can overtake Canada with a win against the defending champions. The Czech Republic occupy third spot on four points after playing all four games.
All five teams from the group advance to the last eight, where the seedings will be determined by their final placing in the standings.
Sweden top Group B, Germany in second
The Swedes won all four games to finish first in Group B on 12 points, with the top three sides advancing to the last eight.
Germany end with eight points, two ahead of Italy, with both sides already assured of their place in the last eight before Tuesday's puck drop. Japan ended with three points and France one, as both countries were eliminated.
After a scoreless opening period, the Italians took the lead 21 seconds after the interval at Milano Rho Arena. With many fans still returning to their seats, Justine Reyes scored following a face-off, tipping Anna Caumo's initial shot into the net.
Germany had a chance on a power play, but the Italians killed the penalty, and Nadia Mattivi raced from the penalty box, collected the puck and passed to Matilde Fantin, whose shot rattled off the post.
The Germans tied it in the second period, Emily Nix forcing the puck home from inside the crease. With less than two minutes remaining, Laura Kluge netted the winner to silence the large Italian support.
Sweden took the lead in the sixth minute through Hanna Thuvik's rebound goal off a save of a shot by Sara Hjalmarsson.
The goal came seconds after Swedish forward Hilda Svensson limped off the ice and down the tunnel after being sent crashing into the boards by Japan's Ayaka Hitosato.
Josefin Bouveng doubled Sweden's lead six minutes into the second period. She took a long pass into the neutral zone from Jenna Raunio and put the puck in off the post.
The Swedes netted late in the second period through Mira Hallin, and Hanna Olsson added a fourth goal on a power play early in the third, her second goal of the Games.
All five teams from the group, which also includes the Czech Republic, advance to the knockout stage, where the seedings will be determined by their final placing in the standings.
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