The White Sox traded Dominguez, Nolan Jones and Boston Smith to the Mariners on Saturday in exchange for Luis Castillo, Jeff Passan of ESPN.com reports.
Dominguez opened the season as the closer for the White Sox but lost his grip on the job in late June. He'll now head to Seattle, where he'll presumably operate in a leverage role for the Mariners with Andres Munoz locked in as the closer. Dominguez has a 4.10 ERA, 1.37 WHIP, 12 saves (in 17 chances), four holds and a 45:23 K:BB over 37.1 innings this season.