Washington went into the match on a run of three successive defeats and made a horrible start when Sav Rocca's punt was blocked by Rashad Jennings early on, allowing Jeremy Stevens to scoop up for a touchdown.
The Redskins responded early in the second quarter thanks to David Amerson, who intercepted Ryvera's stray pass before running 45 yards into the end zone.
Griffin then found his range to nudge Washington ahead early in the third quarter, picking out Pierre Garcon for a vital touchdown pass under pressure.
Washington's defense then stepped up to keep Oakland quiet on offense, with Flynn sacked seven times in total.
Flynn's final sack led to the score that ultimately proved decisive, as Roy Helu's 14-yard dart made sure of a win on the road for the Redskins.