The first week of the World Cup is arguably the best: three matches a day, none at the same time. It is Soccer Christmas for futbol fans, and it's hard to get much work done at the office.Each team takes the pitch with fresh legs, ready to show whether its prospects have been over- or underrated. And if this weekend's biggest matches had one lesson, it was that even great teams don't win every game. The Davids showed themselves stronger than expected, and the Goliaths were sometimes weighed down by sky-high expectations.Case in point: World Cup rookie Iceland tied Argentina on Saturday, in what must have felt like a stunning loss for fans of Lionel Messi and La Albiceleste. Sergio Aguero of Argentina scored first, but Iceland soon equalized it.Then Argentina drew a penalty, and Messi stepped up. It seemed like Iceland's luck had run out. But then Messi fired his shot, and Hannes Halldorsson dove and blocked it in one of the tournament's most stunning moments so far.Iceland's football association reported that 99.6 percent of people watching TV in Iceland (pop. 330,000) during the match were tuned in to the game. The match was also reportedly the highest-rated English-language broadcast of the tournament in the U.S., too.Sunday brought two more surprises.Mexico beat Germany 1-0, after a goal in the 35th minute by 22-year-old Hirving Lozano. Germany, which won the Cup four years ago and is ranked No. 1 in the world, kept pushing but never scored. While such an outcome is rare for Die Mannschaft, Germans have a word for losing an opening game: Auftaktniederlage.And Brazil, along with Germany a favorite to win the whole thing, found itself with a disappointing 1-1 tie with Switzerland. The greatest match of the tournament so far was Friday's thrilling 3-3 draw between Spain and Portugal, featuring a hat trick by Ronaldo. Today's matches so far haven't brought such shocks, but they pave the way for exciting showdowns to come.Sweden beat South Korea 1-0 with a successful penalty kick. The most interesting part of the match was the spycraft that preceded it, with one of Sweden's coaches admitting he had been observing closed Korean practices, and the Korean manager revealing that he had made his players swap shirts during recent friendly matches to confuse their opponents. "They might know a few of our players but it is very difficult for Westerners to distinguish between Asians and that's why we did that," he told reporters.In the day's second match, Belgium took on Panama, which qualified for its first World Cup in part because of the U.S. team's disastrous loss to Trinidad and Tobago. Panama is ranked No. 55 in the world, while Belgium is ranked third. Leading into the match, Panama's coach kept expectations in check."We've become strong on defense. It's Panama's virtue," Hernán Darío Gómez told reporters. "Panama isn't a team that will score a lot of goals. We may create good chances in some matches, but we aren't able to score. We arrive at the World Cup with problems scoring the goals."His assessment was accurate: Panama lost, 0-3, to Belgium.Two of Belgium's goals were scored by Romelu Lukaku: one a diving header, the other an artful chip over the keeper.It was a great showing by the Manchester United forward, who shared his story of growing up poor and black in Belgium in an essay yesterday for The Players Tribune.