The Supporters' Shield-winning Seattle Sounders face FC Dallas in the Western Conference semifinals, beginning on Sunday night. The first leg will be at Toyota Stadium, and the return match will be hosted at CenturyLink Field the following weekend.

There have only been six Supporters' Shield winners that have gone on to win the MLS Cup, per ESPN FC. Seattle will be hoping to make history and become the seventh side to accomplish the feat.

Here are the keys to this Western Conference semifinal matchup.

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