United (3-4-1) ended a two-game losing streak and picked up its first victory since April 16.
Davies set up Josh Wolff in the penalty area for a close-in goal in the 31st minute and then scored his sixth goal of the season in the 52nd minute.
Seattle's goal came in the 71st minute on a penalty kick from Brad Evans after Fredy Montero had been hauled down in the area.
Seattle (3-3-3) had a six-game unbeaten streak come to an end.
Jordana Brewster on Paul Walker: 'He was an enormous presence in my life'
Gal Gadot cast as Wonder Woman for 'Batman vs. Superman'