SEATTLE — With the top spots in the Western Conference still up for grabs, Seattle Sounders FC fans are lining up for a chance to watch the expansion team attempt to make history. This Saturday’s match against FC Dallas will give the fans one last opportunity to show their appreciation of Seattle’s inaugural season, which to date has netted them one major trophy (the Lamar Hunt U.S. Open Cup) and a berth in the playoffs. And depending how things shake out, Sounders FC could grab one of the top two spots in the Western Conference, which would mean a potential home game in the conference championship. In front of a consistently packed Qwest Field, that could be a huge advantage. “It’s truly the one place — not to make it a cliché — you truly feel like you’re watching a game in Europe,” said midfielder Pete Vagenas.