Mamadou Diallo scored four goals against the Galaxy inside Giants Stadium on June 16, 2002. The 22,071 fans at the match sat sprinkled around the cavern. There was room to put a jacket on a nearby seat and stretch out a bit.

Sunday’s Eastern Conference semifinal match against DC United, which the Red Bulls won 1-0 to advance to the Conference Finals, drew 25,219 people to Red Bull Arena. Just 3,000 more than that random game thirteen years earlier. It’s funny how, out of context, the similar attendance figures mask the tremendous contrast between the MLS experience in 2002 and 2015.

I don’t remember that 2002 match that well — I was only 14 then — but I imagine Diallo’s goal celebrations echoed off the 50,000 empty plastic seats. A small group of super fans — odd European posers, I thought — stood behind one net and chanted in those early years. I guess it was aspirational fandom. The groups didn’t even fill up a whole section and the rows on either side remained barren. It all seemed forced to me and I was bored by those MetroStars games. I have, however, come to admire the commitment of those supporters. Their passion has blossomed — the Red Bulls are for real and they were in on the ground floor.

These days, especially in the playoffs, the match experience feels authentic and exciting. The club hands out cool match-day posters. People tailgate throughout Harrison’s parking lot patchwork. The supporters’ clubs gather at events in the Ironbound before marching to the stadium to unfurl giant tifos like this one:

The games begin inside a cloud of smoke thanks to the elaborate pregame pyrotechnics. The haze doesn’t lift for several minutes. Must feel a little like a Phish concert.

The traditions, like the crowd screaming RED! during the national anthem or the unflagging energy of the supporters’ clubs, don’t seem manufactured. I used to count the different teams and countries I would see represented at Red Bulls games as recently as 2010. I think I saw more Barcelona, Brazil and Man U shirts than Red Bulls’. It was like we American soccer fans believed that we had to throw on whatever soccer jersey we owned to prove we were fans of the sport.

We have definitely outgrown that concept. A large proportion, maybe a majority, of fans wear NY Red Bulls branded apparel to matches. You can find that stuff easily at Modell’s or Sports Authority now. Many fans raise scarves during the lineup announcement. People know the chants, the players and the history, including the names in the club’s ring of honor. Several of those stars used to visit our youth soccer tournaments to sign autographs and recruit fans. Rhett Harty signing soccer balls in Mt. Olive, NJ — those were the grassroots days.

The MLS and the Red Bulls have flourished in the thirteen years since Diallo’s four-goal game. There isn’t enough room in the hallways at Red Bull Arena at halftime. We’re all crammed together trying to buy beer or food or a new hat.

How will American soccer expand? Where will the league go in the next thirteen years?