Seattle was finally awarded a Major League Soccer franchise in 2007 . The Sounders debuted in the league in 2009 , winning the US Open Cup . The Seattle franchise also reached the Western Conference semifinals . The Sounders played at Qwest Field , and had an average attendance of approx .
Seattle was finally awarded a Major League Soccer franchise in 2007 . The Sounders debuted in the MLS in 2009 , winning the U.S. Open Cup . The Seattle franchise also reached the Western Conference semifinals . The Sounders play at Qwest Field , and had an average attendance of 30,897 .