While the majority of the North American football community were focused on the 'Debutants Derby' in Florida, it was the Sounders who produced Sunday's best performance, knocking off Eastern Conference play-off winners New England.
Seattle's front two - Clint Dempsey and Obafemi Martins - were again in the thick of the action for Sigi Schmid's side, as they scored all the goals at CenturyLink Field.
The Sounders had the best regular season record last season, claiming 64 points to win the Supporters' Shield for the first time in their history, although they missed out on the MLS Cup final by going down to eventual champions Los Angeles Galaxy in the play-offs.
But in their return to MLS action, Seattle produced the biggest win of 2015's opening weekend.
Dempsey won and converted a penalty in the 25th minute, while Martins headed Tyrone Mears' cross into the net four minutes before half-time.
In the 67th minute, the Sounders' strike-pairing combined with Martins squaring the ball to his captain and Dempsey rolled his shot into an empty net.
The win took Seattle straight back to the top of the Western Conference and the Supporters' Shield standings after no other team managed to win by more than two goals.
At the Citrus Bowl, MLS debutants Orlando City and New York City produced a 1-1 draw in front of a record crowd of 62,510.
The famous American football stadium in Orlando had never seen a larger attendance for a round-ball fixture but the majority of the crowd looked set to go home unhappy after Mix Diskerud gave New York the lead in the 76th minute.
Orlando had the better of the possession and shooting stats throughout the game with their star captain Kaka overshadowing the visitors' own famous skipper David Villa.
But Villa looked set to steal the points for New York when he teed up Diskerud and then tempted Orlando defender Aurelien Collin into a red-card tackle in the 83rd minute, only for Kaka's deflected free-kick to level the match in stoppage-time.
In Sunday's other game, Sporting Kansas City survived Matt Besler's 70th-minute red card to draw 1-1 with New York Red Bulls.
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