After delivering a near flawless special teams effort in a season opening win over Jacksonville, Mike Priefer's unit had its struggles in last week's upset of San Francisco. The Vikings special teams coordinator met with reporters Thursday and offered his diagnoses for a handful of things that went wrong against the Niners.

Yes, there were the huge second half kickoff returns by San Francisco's Kyle Williams, one for 94 yards and another for 50. And Priefer offered his general assessment of what went wrong with his coverage on those.

"Number one, they blocked us up well," he said. "We knew going in they were very good at it. And we did not do a great job with our lane integrity."

But a couple of more minor mistakes had Priefer equally aggravated. Take Chris Kluwe's first punt of the day, for example, a wobbly 35-yarder in which his drop was too far inside.

And then there was Kluwe's best punt which came with 13:19 left and the Vikings protecting a 24-13 lead. From the 42, Kluwe bombed a perfect directional kick that landed just a couple yards in front of the right pylon with cornerback A.J. Jefferson coming off a block well and blazing down the sideline with a chance to down the ball inside the 2. Instead, Jefferson got to the punt, corralled it but dropped it on the goal line for a touchback, costing the Vikings valuable field position.

"That's a heartbreaker right there," Priefer said. "[Jefferson needs to] throw it back a little further. Or even if you're near the sideline, we've talked about knocking it out of bounds. And A.J. hasn't been around us. I mean, he was coached well at Arizona, don't get me wrong. But there are little minute detail things that we talk about all the time that the more he hears it, the better he'll respond."

Around the block

Priefer was much more pleased with the special teams effort at the close of the first half with Letroy Guion blocking a 43-yard David Akers kick with 52 seconds left and rookie Blair Walsh capitalizing a few moments later by nailing a 52-yard field goal of his own. Instead of holding a 14-6 halftime advantage, the Vikings led 17-3.

"Huge swing against a very good football team," Priefer said. "It gave us a lot of momentum going into the half."

As for Guion's big moment? The energetic defensive tackle combined with Matt Kalil to get great push against the 49ers' front. And it's Priefer's belief that had Guion not got his hand on Akers' kick, Kalil would have.

"Letroy comes off the ball so hard and so low and he's got great timing," Priefer said. "Being a defensive lineman, it's a little bit easier for him than it is for a guy like Matt Kalil, who's obviously going off a snap count. So our goal is to get Matt even better with his get-off and have those two working together and continuing to work together as the year goes on."

Green light

If it seems like Percy Harvin has no caution when fielding kicks deep in his own end zone and bringing them out, that's by design.

"Overly aggressive is not a term [with us]," Priefer said. "We're going to be aggressive. We're going to get after it. And we're going to bring it out when we have an opportunity to bring it out. And the only way we keep him in is determined by a situation. Up by 10, 4 minutes left to go in the game, let's give the ball to the offense at the 20, try to grind it out in the 4-minute situation and give us the best field position we can. But I'll be honest with you, I think with our returners back there and the guys we have blocking for them, we have a chance to score every time."

Harvin caught one kick against San Francisco six yards deep and returned it only to the 14. But that's OK. Priefer wants his kick return unit to have a fearless confidence.

"If I look at Percy and say, 'We need to keep this one in,' he'd look at me cross-eyed. He believes he's going to score every time. And I think the guys around him believe he's going to score every time. We've darn near broke about three this year."

For the year, Harvin has returned eight kickoffs for an average of 30 yards, ranking eighth in the NFL heading into Week 4. The Vikings have taken touchbacks on five of the 17 kickoffs they've received.

He keeps going and going and going …

Priefer hasn't needed much time this week to review the strengths and weaknesses of Lions kicker Jason Hanson, who's been booting balls in Detroit since 1992. Hanson is in his 21st season now. And last week, after punter Ben Graham suffered a season-ending calf injury, Hanson was called into emergency duty as a punter as well. Hanson's busy day in Tennessee included three punts for an average of 39.3 yards. He also added field goals from 47, 53, 33 and 26 yards and made three extra points.

Hanson was reportedly unhappy with his punting effort.

"He didn't think they were good punts," Priefer said. "I thought they were outstanding punts. They were high, short and really unreturnable. Fair catch balls. And he had one inside the 20. Nothing he does anymore surprises me. He's kind of like a Hall of Fame guy to me."