As the Vikings did their final preparations for their season opener against the San Francisco 49ers, coach Mike Zimmer took stock of his players during the Monday morning walk-through at the team hotel and felt certain they were ready to roll after a strong preseason and a sharp week of practices leading to kickoff.

"I was confident going into the ballgame," Zimmer said. "I said, 'Man, these guys are ready to go.' So much for that."

The Vikings most certainly were not ready, squandering a pair of early offensive opportunities and getting manhandled on both sides of the ball as the game went on. At night's end, they boarded a red-eye flight back to Minneapolis with a disappointing 20-3 loss and even more concerns than they had before heading to the West Coast.

In the immediate aftermath of the loss, Zimmer was disgusted, at one point saying he hopes to field a Vikings team like the one that just bullied them on national television. And after reviewing the tape on that long, quiet plane ride home, Zimmer didn't see much to change his opinion.

"It was a poor performance. Disappointing. We did not play together as a team in most all phases, and we've got a lot of soul-searching to get done," Zimmer said.

Complicating matters is that the Vikings get only five days to come up with answers before their now-critical game against NFC North rival Detroit Lions on Sunday.

After losing starting center John Sullivan and right tackle Phil Loadholt during the preseason, the Vikings knew that their offensive line would be tested.

They also knew they would need to prove that they could stop the run after ranking 25th in the league in that category in Zimmer's first season.

And whether they admitted or not, of course the right leg and psyche of kicker Blair Walsh were concerns after he missed six preseason field-goal attempts.

But all the missed tackles and blown assignments and double-wide running lanes on defense? The ineffectiveness of running back Adrian Peterson? The shaky play of quarterback Teddy Bridgewater? Zimmer didn't see that coming.

"I told the team at halftime 'I don't even know who is out there today. I don't even know who this team is. I've never seen this side of us before. Never,' " said Zimmer, who put this loss right up there with last year's 42-10 drubbing at Lambeau Field.

Peterson rushed for 31 yards on 10 carries in his return to the field after a yearlong layoff. After the game, the 30-year-old mentioned that he felt tentative at times. But Zimmer saw a running back that actually was too eager to hit the hole.

Bridgewater, meanwhile, was uncharacteristically erratic and lacked poise in the pocket, at one point scrambling directly into rookie right tackle T.J. Clemmings. Zimmer said it was the first time he has thought the 22-year-old looked rattled.

"Usually he's got so much composure," Zimmer said. "But he did seem that way."

And the play of his defense, which was gouged by the 49ers for 230 rushing yards, still had Zimmer flabbergasted as of Tuesday afternoon. San Francisco's offensive line pushed his front seven around, and 49ers back Carlos Hyde hurt the Vikings on both stretch runs to the outside and several clever cutbacks against the grain.

"We jumped inside blocks a lot. We ran underneath blocks. We didn't fit in the right place a lot of times," Zimmer said. "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."

Zimmer was not pleased with the linebacker play. And he said the safety spot next to Harrison Smith is "a fluid situation" after he gave Andrew Sendejo the start but saw enough gambling from Sendejo to go right back to Robert Blanton.

While Zimmer and the Vikings are mulling their options when it comes to their defensive personnel, they say they still are not giving any consideration to bringing in competition for Walsh, who missed from 44 yards in the scoreless first quarter.

One game into the season, a Vikings team that has been hyped as a potential playoff team already has plenty of issues. Still, despite knowing about many of them heading into Monday night, Zimmer still can't believe the way the Vikings got dominated.

"No, there was no indication whatsoever," Zimmer said.