The England captain, the subject of intense transfer speculation following bids from Manchester City, retained the skipper's armband as Chelsea manager Carlo Ancelotti sent out his first side since taking over from Guus Hiddink at the end of last season.
First-half goals from teenage debutant Daniel Sturridge and England midfielder Frank Lampard were enough to see off a Seattle team led by Freddie Ljungberg in their inaugural Major League Soccer season and watched by a crowd of 65,289.
Sturridge, 19, was handed a starting role alongside Nicolas Anelka in the Chelsea attack following his summer move from Manchester City and he needed just 12 minutes to get on the scoresheet for his new club.
He collected a Florent Malouda chip over the top of the Sounders defence, checked his run down the left channel to beat defender Tyrone Marshall and curled home right-footed across Seattle goalkeeper Kasey Keller.
Lampard doubled the lead in the 35th minute after Jose Bosingwa had cut in from the right to send Anelka into space on the byline, the Frenchman cutting the ball back for the midfielder to slot home.
Seattle were not without their chances, former Arsenal star Ljungberg forcing a fine save from Petr Cech just before Chelsea's second goal from a free-kick 20 yards out. The Blues keeper pushed the ball around the post at full stretch to his right from the Swede's effort.
Ljungberg forced another rearguard action just before half-time with a low drive from in front of goal and through a crowd of players that Cech blocked after Bosingwa's diving body had taken the pace off the shot.
Ancelotti kept his promise to make multiple substitutions during Chelsea's first pre-season outing and he made nine changes at half-time, retaining just Lampard and Michael Ballack from the starting line-up.
Seattle made four changes and the home side made the brightest start to the second half, Chelsea keeper Hilario flapping at a Ljungberg corner that reached sub Zach Scott at the back post. The Sounders full-back outjumped Ricardo Carvalho but sent his header past the upright.
There was further trouble for Chelsea at the back when Hilario's attempted clearance was charged down by Sebastien Le Toux in the 69th minute and ran just past the post, while minutes later Sanna Nyassi got behind the Blues defence and sent a chip onto the roof of the net.
Lampard even managed to get booked in stoppage time for a foul on Nyassi as the Blues saw out the game with a clean sheet to give Ancelotti a winning start to his Chelsea reign.