MANKATO - The No. 1 rule for any NFL preseason game is never, under any circumstances, overreact and make sweeping generalizations about what happens, good or bad.

With that in mind, here is one man's reasoned reaction to the Vikings' 17-6 loss to the San Francisco 49ers on Friday night:

WHERE ON EARTH WAS THEIR STINKIN' RUN DEFENSE?!

"We'll be fine," defensive coordinator Alan Williams declared Monday.

Feel better? For a while, their performance sure looked and felt like 2011 all over again. Except this time they couldn't stop the run instead of the pass.

The 49ers rushed for 260 yards, including 198 in the first half. The Vikings missed assignments, took poor angles and basically made a mess of their preseason debut. Williams, however, didn't sound overly alarmed as he dissected it.

"Saw a few misfits [in assignment], a few bad angles to the football," he said, "but I also saw some good things."

Veterans Jared Allen, Kevin Williams and Antoine Winfield got the night off, so that had an obvious effect. Nose tackle Letroy Guion suffered a minor knee injury on the first series, and key starters played minimally. Preseason openers are always an adventure into the unknown, but the Vikings did nothing to alleviate concerns about their ability to stop an opposing offense.

"You don't like it if you give up 260 yards rushing no matter if it's a practice, [preseason] or real game," Allen said. "From that standpoint, it was disappointing."

Allen insisted the mistakes are all "fixable." The Vikings certainly hope so. Their failures in the secondary last season resulted in unsightly ineptitude in pass coverage, but their run defense revealed warts as well.

The Vikings finished 11th in the NFL in rushing defense last season, allowing an average of 107 yards per game. That was their highest average -- and first time they finished outside the top 10 in that category -- since 2005.

The pass defense should be markedly improved this season -- it can't be any worse, right? The return of Winfield and Chris Cook at cornerback and the arrival of rookie safety Harrison Smith upgrade that area.

The front seven is a different story, particularly the teeth of the defense. Just like in baseball, football teams want to be strong up the middle, and the Vikings alignment consists largely of unproven talent in Guion, middle linebacker Jasper Brinkley and a group of young safeties.

Guion has started only three games in four seasons. Brinkley spent last season on injured reserve. In their first preseason action, Guion injured his knee and Brinkley looked tentative and rusty. Again, Williams tried to spin it as a positive.

"They are coming along, just need more reps," he said. "It has been a little bit since Brinkley has been on the field full speed. Actually the way he played and the way they were up the middle, I felt encouraged about what we have."

Brinkley is a thumper. He loves to hit. No one questions his ability to play physical, but he was handed a starting job at a critical position after being sidelined for an entire season because of a hip injury.

"With any guy that's been out for a year there's going to be some rust," Williams said. "He's knocking it off and coming along just like we thought he would. We're pleased with Jasper."

The NFL has evolved into a passing league, so maybe run defense isn't as important as it once was. But a defense still needs to be able to hold its ground when the situation calls for it. The Vikings lived for those moments a few years ago.

It was always entertaining watching an offense try to run the ball on Pat Williams, Kevin Williams, E.J. Henderson and the rest of that crew. Those Vikings defenses were susceptible through the air, but they hardly budged against the run.

Their creed became a "blade of grass." Give them a blade of grass and they would defend it. They succeeded most times, which usually caused Big Pat to spout off like a pro wrestler in his own unique and colorful way.

No doubt he'd have some choice words for the defense after Friday's effort. What we don't know yet is whether that was merely a bad first outing minus a few key starters in a preseason game, or a sign of things to come.

Chip Scoggins • ascoggins@startribune.com