If history is any guide, you can never rule out the unexpected in the final four. This year, the U.S. remains the underdog, facing the defending champions from Canada. It's hard to classify the host Russians as underdogs with their dynamic offensive talent, although they are battling the tournament's only undefeated team in Finland.

Here are five examples of semi-final upsets since the IIHF instituted the playoff system in 1992. As you'll see, almost all involve either Finland or Slovakia. It's an interesting phenomenon, as the Finns have trended upwards this decade, while the Slovaks have settled for a few surprising medals.

9 May 1992: Finland 3, Czechoslovakia 2

Jarkko Varvio scored the shootout winner in Prague as Finland ousted the host nation and advanced to the final against Sweden. Nowadays, this scenario would hardly be considered an upset. But at the time, the Finns had never won an IIHF Ice Hockey World Championship medal of any shade, dating back to their 1939 debut.

Coach Pentti Matikainen's squad wound up taking the silver with a 5-2 loss to Tre Kronor. Varvio tied with Mikko Makela for the tournament scoring lead (10 points) on a squad that also included an 18-year-old Jere Lehtinen. The Czechoslovak team they edged in the semi-final featured a lot of well-known Roberts: Robert Reichel, Robert Lang, and Robert Svehla.

12 May 2000: Slovakia 3, Finland 1

At the first IIHF Ice Hockey World Championship ever held in St. Petersburg, Russia, the Slovaks found themselves in the same boat as Finland eight years ago - questing for their first Worlds medal. Since debuting at the top level in 1996, they'd finished 10th, ninth, seventh, and seventh. So beating the Finns in the semis was huge.

Captain Miroslav Satan, who'd finish the tournament with 10 goals and two assists and be named Best Forward, scored the first-period winner. "I wasn't nervous at all before the game," said Slovak goalie Jan Lasak. "I should have been, but I felt very calm. I knew we would not lose tonight." The opportunistic Slovaks, however, fell 5-3 to their big brothers from the Czech Republic in the final.

9 May 2002: Slovakia 3, Sweden 2

It was a surprise when Zigmund Palffy scored in the shootout to lift the Slovaks to a 3-2 victory over host Sweden. Granted, everyone could see in the early 2000's that Slovak hockey was on the upswing. But by the same token, this Slovak team had needed to rally from a 2-0 deficit to beat Canada 3-2 in the quarter-final. And Tre Kronor had loaded up on talent for this tournament in Gothenburg. The goal was to make up for the devastating 4-3 quarter-final defeat against lightly regarded Belarus at the Salt Lake City Olympics back in February.

However, even with stars like Markus Naslund, Michael Nylander, and Ulf Dahlen in the lineup, the Swedes fell short again in front of 10,854 spectators at the Scandinavium. They'd settle for beating Finland for bronze, while Peter Bondra got the late 4-3 winner against Russia in the final to give the Slovaks their first gold medal ever.

12 May 2007: Finland 2, Russia 1

Mikko Koivu's overtime winner dealt Russia its first loss ever on Moscow ice in five World Championships (1957, 1973, 1979, 1986, 2007). For Russian hockey fans, it was a stunning and dark moment. To that point, their stacked team featuring Alexander Ovechkin, Ilya Kovalchuk, and Yevgeni Malkin had gone undefeated.

At the Khodynka Arena, Malkin opened the scoring on a first-period power play and Jukka Hentunen tied it up less than four minutes later for coach Erkka Westerlund's team with a shorthanded goal.

The deciding goal came on a gaffe by Russian goalie Alexander Yeromenko. He attempted to pokecheck Koivu, who evaded him and slid the puck into the wide-open net at 5:40. "It's always tight when you go to overtime, so it's a good feeling," Koivu said.

The jubilant Finns couldn't carry their momentum over to the gold medal game, though, as they lost 4-2 to the Rick Nash-led Canadians.

18 May 2013: Switzerland 3, United States 0

Based simply on Switzerland's results at the 2013 tournament in Stockholm, you wouldn't call the semi-final victory over the Americans an upset. The Swiss had been red-hot from the get-go, starting off with consecutive wins over the host Swedes, Canada, and the Czech Republic. In fact, they'd won eight straight (one in OT) heading into the semis.

But historically speaking, it was a thoroughly anomalous performance by Switzerland, which had finished ninth in 2011 and 11th in 2012. In fact, the Swiss have not qualified for the quarter-finals again since the magical run of 2013

In the 3-0 win over the U.S., Nino Niederreiter led the way with two points, including the winner midway through the second period, and goalie Reto Berra earned a 29-save shutout. "I think it's the biggest win since a long, long time for Switzerland," said Berra. "Also, I think for a lot of players, it was the most important game in their life today.”

The Americans were no slouches that year. They eliminated defending champion Russia with an 8-3 quarter-final rout. They had a goaltending duo of Ben Bishop and John Gibson, and Paul Stastny placed second in tournament scoring with 15 points. While the Swiss took their first silver medal since 1935 with a 5-1 final loss to Sweden, the Americans would claim bronze on Alex Galchenyuk's 3-2 shootout winner versus Finland.