Like their Pacific Northwest rivals, the Sounders' NASL tradition (1974-83) and longstanding lower-level rivalries gave the club a bit of a head start when it joined MLS in 2009. That was no guarantee that they'd be more popular than their next-door neighbor at Safeco Field, but baseball's Mariners are bringing in nearly 15,000 fewer fans per game than the Sounders. Considering neither the Sounders, Whitecaps or Timbers were in the league three years ago, MLS' Northwest-navigated attendance boost seems well overdue.

"The passionate fan base has always been there, but in some cases it was the stadium or an ownership group," Courtemanche says of the teams, which count Microsoft ( MSFT)-founder and Seattle Seahawks owner Paul Allen, former Yahoo! ( YHOO) Chief Operating Officer Jeff Mallett, Phoenix Suns point guard Steve Nash and Price Is Right host Drew Carey among their owners. Qwest Field in Seattle, now CenterLink Field, wasn't built until the late 1990s and Jeld-Wen park, formerly Civic Stadium, was more of a baseball facility and underwent a $35 million renovation to host a Major League Soccer team, he says.

It's only fair to note that the Mariners and other major league baseball teams play 162 games per season compared with 34 for Major League Soccer. That said, the Sounders would have the ninth-highest attendance in baseball if they managed the same average in the majors.

It's no small feat for a league that contracted its counterparts to baseball's Marlins and Rays -- the Miami Fusion and Tampa Bay Mutiny -- in 2001, had no television contract and shrunk to 10 teams playing mostly in outsized football stadiums. Today, the league has 18 teams; television deals with ESPN ( DIS), Fox Soccer ( NWS) and Univision; and a fan base that's growing in all the right demographics.

Roughly a third of MLS fans are Hispanic, Courtemanche says, and are increasingly drawn to the league as it brings in stars from 60 countries -- including New York defender and Mexican national team captain Rafael Marquez, 19-year-old Colombian forward for FC Dallas Fabian Castillo and his countryman and Seattle Sounders striker Fredy Montero, who's given Seattle a lot to cheer about lately. It also benefits from a coveted 18-to-24-year-old fan demographic that's a lot more familiar with Major League Soccer than the generation before.

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