MINNEAPOLIS -- The Minnesota Vikings and their defensive-minded head coach spent all offseason focusing on improving a run defense that was among the worst in the league.

After getting run over by Carlos Hyde and the San Francisco 49ers in the season opener, a humbled defense reconvened on Wednesday with few answers for what went wrong.

"Honestly, they ran maybe two or three plays over and over again," linebacker Anthony Barr said. "We just couldn't stop it. It was simple. We knew it was coming, we just couldn't stop it. So we've just got to take a deep look within and figure it out."

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Hyde racked up 168 of the 49ers' 230 yards on the ground, a dominating effort in a 20-3 victory that wasn't really that close. The Vikings offense struggled mightily as well, but Zimmer was at a loss when trying to find justification for the undisciplined performance by a defense that was determined to put the embarrassments of last season behind it.

"We did a lot of uncharacteristic things there," Zimmer said. "We jumped inside blocks a lot, we ran underneath blocks, we didn't fit in the right place a lot of times, we didn't tackle good, we didn't get off blocks, we had one guy making the tackle a lot of times, which is ridiculous."

The Vikings gave up 121.4 yards rushing per game in Zimmer's first season, ranking them 25th in the 32-team league. They didn't make significant changes to their front seven in the offseason, concentrating more on improving the group that they have and increasing their understanding of Zimmer's system in Year 2.

Andrew Sendejo was a surprise starter at safety opposite Harrison Smith, but Zimmer pulled him as the game went on in part because of his difficulties in supporting the run. Robert Blanton, who was believed to be the front-runner for the starting job when the Vikings finished the preseason, didn't fare much better.

Gerald Hodges is the new starter at middle linebacker, and the eager youngster was out of position at times while trying to make the big play. Zimmer was asked if he considered going more to rookie second-round draft pick Eric Kendricks.

"He didn't play that good either," Zimmer said. "It was equal opportunity (Monday) night."

The starting defensive line of Brian Robison, Everson Griffen, Sharrif Floyd and Linval Joseph is entrenched, and the linebacker corps of Barr, Hodges and Chad Greenway is the most experienced combination possible.

But Zimmer didn't appear to be contemplating any big changes anyway. He said he didn't recognize the group that showed up on the video he reviewed and figured the sting of that beating would refocus his players.

"We've got a lot of soul searching to get done," he said.

The Vikings host Detroit on Sunday in their home opener. The Lions have a high-flying offense with Matthew Stafford and receiver Calvin Johnson, but rookie running back Ameer Abdullah averaged 7.1 yards per carry and scored a touchdown in their season-opening loss in San Diego.

"We practiced way too hard to go out there and put a show on like that," defensive end Everson Griffen said. "It's embarrassing, and we should take it personal. I take it personal. And we're going to go out there and we're going to do our job, and that's all I can say, and I'm done here."