MINNEAPOLIS — Matt Cassel has won the Vikings starting quarterback job. Now, the fight is to keep it. Minnesota coach Mike Zimmer, as expected, named Cassel on Monday the starter for the Sept. 7 regular-season opener at St. Louis. He had been battling rookie Teddy Bridgewater. Bridgewater already has heard fans chant his name during preseason games, and they will clamor for the first-round pick out of Louisville if Cassel has a bad game, or even makes a bad play.