The World Cup is the most-watched sporting event on Earth, with nearly a billion expected to watch it in five action-packed weeks.

And even many of America's most-watched people get into the sporting spirit for the tournament, especially when Team USA is on the pitch. The underdog squad is coming off a big win against Ghana and will play its second match of the 2014 World Cup in Brazil Sunday against Portugal.

While there will be some bona fide celebrities actually playing in the much-anticipated showdown -- Cristiano Ronaldo, for instance -- non-soccer stars from around the world are expected to tune in as well.

When the USA team beat Ghana 2-1 last week, the outpouring of online support included messages from a wide range of famous folks, many of whom will likely be watching the Portugal match Sunday evening either from home or from the stands at Arena da Amazonia in Manaus, Brazil.

Here's a rundown of some of the dozens of celebrities who tweeted messages of support and celebration during or after the USA-Ghana contest: