The Seattle Sounders are on track for the greatest season by any club in MLS history.

They'll walk into PPL Park for Tuesday night's 2014 US Open Cup final against the Philadelphia Union (7:30 pm ET, GolTV) as the current Supporters' Shield leaders and one of the early favorites for MLS Cup.

If they succeed in defeating the Union, it would mark the first step toward a historic treble: three trophies in a single season. While there have been plenty of "doubles" over the course of MLS history, the treble has proven elusive.

Of the 10 MLS sides that have claimed the "double" -- a combination of two of the following trophies: MLS Cup, Supporters' Shield, US Open Cup -- the three teams that came the closest to capturing a treble were D.C. United (1997), the LA Galaxy (2002) and the Chicago Fire (2003). Each of those teams won two trophies and got to the finals in a third tournament.

Below are all 10 double winners in MLS history and how they fared in each of the four competitions in which they competed. D.C. United's triumph in the 1998 CONCACAF Champions Cup and its subsequent 1998 Inter-American Cup were not considered for purposes of this list.

Team MLS Cup Supporters' Shield US Open Cup CONCACAF 1996 CHAMPIONS 3rd PLACE CHAMPIONS DID NOT PARTICIPATE 1997 CHAMPIONS CHAMPIONS FINALIST SEMIFINALIST 1998 CHAMPIONS 3rd PLACE CHAMPIONS DID NOT PARTICIPATE 1999 CHAMPIONS CHAMPIONS 3rd ROUND SEMIFINALIST 2000 CHAMPIONS CHAMPIONS 2nd ROUND DID NOT PARTICIPATE 2002 CHAMPIONS CHAMPIONS FINALIST DID NOT PARTICIPATE 2003 FINALIST CHAMPIONS CHAMPIONS DID NOT PARTICIPATE 2005 CHAMPIONS 9th PLACE CHAMPIONS DID NOT PARTICIPATE 2008 CHAMPIONS CHAMPIONS QUALIFICATION ROUND DID NOT PARTICIPATE 2011 CHAMPIONS CHAMPIONS QUARTERFINALIST QUALIFYING ROUND*

* Note: The Galaxy were knocked out of the 2010-11 CONCACAF Champions League during the qualifying round in 2010, thus eliminating the Galaxy from the knockout rounds played the following year in 2011.