Dallas (5-1) outdistanced Seattle (3-2) handily in yards (401-206), first downs (23-9), and TOP (37:39-22:21) on their way to a 30-23 road win over the defending champs.
DeMarco Murray topped 100 yards for the sixth straight week, while the reborn Rolando McClain ensured the Cowboys' upset with a late interception of Russell Wilson.
The Seahawks fell a game behind Arizona (4-1), which bounced back from last week's blowout in Denver with a 30-20 win over visiting Washington (1-5).
Carson Palmer made a triumphant return from his shoulder injury, throwing two touchdown passes in a turnover-free performance.
Dallas and San Diego have each won five straight and remain the only teams with better records than Denver and Arizona, while Philly is also 4-1 heading into its Sunday night matchup with the Giants.