The rebirth of a regional rivalry in the Pacific Northwest has shifted Major League Soccer’s center of attention, and gravity, to the west.

M.L.S., a league run by a native New Yorker with offices in Midtown Manhattan, begins its 16th season Tuesday night when Los Angeles visits Seattle before a crowd expected to be in excess of 35,000 at Qwest Field. The last two league champions — Colorado last year and Real Salt Lake in 2009 — sit on either side of the Continental Divide. There are three teams in California.

In their two years in the league, the Seattle Sounders have been a resounding success, and will log their 33rd consecutive M.L.S. sellout in the season opener. This year, Seattle (which set a league record with an average attendance of 36,173 in 2010) will be joined by two clubs, the league’s 17th and 18th teams, with names familiar to fans of a certain vintage — the Portland Timbers and the Vancouver Whitecaps.

The three teams are in midsize markets that have limited competition from other major sports — in Seattle, the N.F.L.’s Seahawks and baseball’s Mariners; in Portland, the N.B.A.’s Trail Blazers; and in Vancouver, the N.H.L.’s Canucks. In addition, the Portland area is the North American home to Nike and Adidas, which last year extended for eight years its exclusive sponsorship deal, reportedly worth $200 million, with the league.