The Raiders produced three turnovers on defense and their only touchdown of the game came when Nnamdi Asomugha setup his offense at the Denver 15-yard line.
Oakland could not convert, however, on two Fabian Washington interceptions.
Sebastian Janikowski tied his own franchise record with a 55-yard field goal in the second quarter and added a 20-yard field goal before the half.
Denver took their first lead of the game in the fourth quarter with Plummer going 6-for-6 for 60 yards, capped by a one-yard toss to Kyle Johnson.
Oakland would get the ball again with a minute and 50 seconds on the clock. But Walter fumbled the ball away on what amounted to successive offensive players, ending any chance of a comeback.
Warren Sapp has two sacks in the game to give him six on the year. It is his second multi-sack game of the year.