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The Seahawks played without linebacker Derick Hall and two starting defensive backs: S Julian Love and CBs Devon Witherspoon.
Seattle remains the only major league club without a pennant.
Seattle RHP Luis Castillo starts Game 4 Thursday against RHP Max Scherzer.
The Seahawks stay in the AFC South and host Houston next Monday night.
George Springer homered on the first pitch from Miller, who then escaped a two-on jam in a 27-pitch first inning.
Vince Dunn and Jared McCann also scored for the Kraken, who had gone 0-3-1 in their previous four openers, including a 5-4 overtime loss to Anaheim in 2022.
Game 5 is in Seattle on Friday.
Seattle RHP Bryce Miller are expected to start Game 4 on Wednesday.
Darnold and Mayfield combine for 720 yards, just 10 incompletions
Logan Gilbert scheduled to start game 3 Tuesday in Detroit