Nights like last night are a reminder of just how far from mainstream popularity soccer in the United States actually is, as I watched the Gold Cup semi-final between the U.S. and their neighbour Canada in front of a half-empty Soldier Field on Chicago’s lakefront. The average American could care less that his country was involved in its biggest game since last year’s World Cup, despite the best efforts of Sam’s Army.

But wait: just two hours later, and the second semi-final kicks-off in front of a near packed house full of screaming passionate fans from Chicago rooting for their country. Mexico were playing, and there were plenty there to cheer them on. More after the jump, including plenty of photos that explain things better than my words can.

We’ve seen many articles lately on the hardcore American supporter’s groups, and they were evident again last night in the form of Sam’s Army, a couple of hundred diehard U.S. Men’s National Team followers who were certainly vibrant in their support of the team.

I took many better close-up shots of Sam’s Army, but I chose the one above because it illustrates something interesting about them: they support their team avidly in a pit of deep apathy. The seats around them only began to be filled as the U.S. game headed towards its conclusion – a controversial 2-1 victory – and Mexico supporters arrived for the second leg of the night, Mexico-Guadaloupe. Some fans with their faces painted green and white indulged in seemingly ironic chants of U-S-A; some cheered when the U.S. scored; but the loudest cheers were undoubtedly reserved for Canada’s fightback at the end of the game. Others stood with disinterest around the concourse.

Of course, there were many other U.S. followers around the stadium.

However, the stands only filled as kick-off approached for Mexico’s game against Guadaloupe. Sam’s Army stuck around, but suddenly their stars and stripes stuck out like a sore thumb in a sea of green and white.

A crowd of 50,760 filled most of the stadium; I would guess 80% were Mexico supporters.

Mexico’s fans were out to have a good time. Soccer matches in the U.S. can often lack atmosphere, but one could certainly not say that tonight. It was a tense game on the field – Mexico just sneaking a 1-0 win in an unimpressive display – but everyone seemed to presume Mexico would prevail in the end, with much excitement but little tension evident.

Many fans came dressed in elaborate outfits:

I saw a little trouble flare far away in one stand, good natured ribbing went back and forth, but mostly U.S. and Mexico fans coexisted peacefully. Will it stay that way on Sunday, as the U.S. takes on Mexico in the final? Pitchinvasion.net will be there to find out.