Wannstedt said after the game that Fiedler will start Thursday at Dallas, something that's not a surprise considering Fiedler's performance.
Williams also had a lot of success late, as he recorded only his fourth 100-yard game of the season.
The defense had its problems against the Washington offense, led by backup quarterback Tim Hasselbeck until coming up big in the final quarter.
The victory was clinched when Matt Turk picked up a one-hopper and boomed a long punt that was fumbled by Washington returner Pat Johnson and recovered by Miami.
So the Dolphins now find themselves at 7-4 heading into the Thanksgiving Day game at Dallas.