ALAMEDA — In the flash of a big run by Adrian Peterson or DeAngelo Williams, the Raiders’ once-touted run defense has deteriorated.

“We were doing so good,” defensive coordinator Ken Norton Jr. lamented.

Two weeks ago, Oakland was allowing just 82.9 rushing yards per game, good for second in the NFL, and was coming off a standout performance against one of the league’s top rushing attacks.

But since that stout effort Nov. 1 against the New York Jets, when they held them to 74 yards rushing and top back Chris Ivory to 17 yards on 15 carries, the Raiders have been crushed. They’ve allowed 458 rushing yards the past two games — after giving up a total of 580 the first seven — and now own the NFL’s 23rd-ranked run defense.

“Fundamentals broke down at the wrong times and it just looks so bad,” defensive tackle Justin Ellis explained. “Big runs make it look real bad.”

The Raiders’ last defensive play of the afternoon in Sunday’s 30-14 loss to the Minnesota Vikings was that big run when Adrian Peterson raced 80 yards for a touchdown.

A week before, Williams bounced in and out of holes while powering his way to 170 rushing yards in the Pittsburgh Steelers’ 38-35 win.

“Sometimes you get a little complacent, you think you’re already good at something,” Norton said. “You can’t overlook the things you do well.”

That’s where Norton is putting some of the blame on himself.

“I just need to become a better teacher,” Norton said. “We need to be better as far our fundamentals, Our tackling is something we really (built) our foundation on and somewhere along the way, that failed us.”

The past two weeks have bothered Norton so much because they’ve been a direct attack on what he perceived to be the Raiders’ strength.

“One thing we hang our hat on is: no one runs the ball, no one throws the ball deep on us,” Norton said. “And they attacked us at our foundation of what we do best. So that really set us back a little bit.”

The Raiders have a chance to get healthy Sunday against the Detroit Lions, which own the league’s worst rushing attack at just 66.9 yards per game.

Rookie running back Ameer Adullah has failed to impress, generating just 240 rushing yards. He’s had double digit carries only twice this year and has been limited to seven offensive touches the past two games.

Those modest stats still make Abdullah, a second-round pick out of Nebraska who has excelled as a kick returner, the Lions’ leading rusher.

In recent weeks, Joique Bell has taken over as the primary ballcarrier, but he had only 17 yards on 14 carries in Detroit’s 18-16 win in Green Bay last week.

The Raiders will need to further the Lions’ run game struggles if they want to avoid their first three-game losing streak of the season.

“You can’t take anything for granted,” Norton said. “They’re going to challenge us. We have to make sure that we show them that we’re here to stop the run.”

The Raiders feel as though their run-stopping woes are easily correctable and hope to put that on display in Detroit.

“It’s going to be an easy fix,” Ellis said. “We all saw that it was fixable things. We’ve just got to fix them and keep pushing.”

What might some of those fixes involve?

“You’ve got to stay disciplined,” Ellis said. “You’ve got to do what you got to do. You can’t do no extra because when you do extra, you leave your gap open.”

An extra challenge comes with the absence of Aldon Smith, the Raiders’ outside linebacker who was handed a one-year suspension from the league on Tuesday for repeated substance abuse violations.

Despite his reputation as a pass rusher, Smith had done a good job sealing runs off the edge and developed into one of the team’s best run defenders. Now they have to correct some issues without the services of one of their more talented players.

“I think when we were doing bad and even when we were doing good, it wasn’t because of one person,” Mario Edwards Jr. said. “It was just us beating ourselves, not being in the gap and not being assignment sound.”