SANTA CLARA – Alex Smith and Vernon Davis have made a killing during the past few years on a simple seam route that pits the tight end's speed against their opponent's inside linebacker.

Few have been able to keep pace.

But when the duo tried that play during Saturday's practice, Smith's pass was broken up and Davis ended up sprawled on the grass.

The culprit?

Patrick Willis, who last year took on the role as the 49ers' designated tight end stopper. This year, he's trying to perfect his craft.

Among the tight ends Willis will face this season are Green Bay's Jermichael Finley, Detroit's Brandon Pettigrew, the New York Jets' Dustin Keller, New Orleans' Jimmy Graham and New England's Rob Gronkowski. Gronkowski and Graham finished first and second in receiving yards by a tight end last season, respectively, and combined for 28 touchdowns.

Willis said he's only focusing on Finley, his Week One opponent, for now. But he noted that his warm-up act – covering Davis and fellow tight end Delanie Walker in practice each day – is one of his toughest assignments.

"I feel if I can cover our guys – or cover them pretty well – then there shouldn't be a tight end in the league that I shouldn't be able to cover," Willis said. "So I just work on covering those guys when I have the opportunity."

Crabtree absent – Wideout Michael Crabtree, who never has played in an exhibition game for the 49ers, missed Saturday's practice after apparently turning his ankle late in Friday's session. Crabtree walked off the field under his own power, and the injury did not appear serious.

Crabtree missed the 2009 exhibition season because of a contract dispute, he hurt his neck in 2010 and was dealing with a broken foot at this time last year.

Smith has cited Crabtree's good health this season as one of the reasons he is optimistic the two will have a big year.

"He had such a great spring and summer," Smith said Friday. "I think just keep doing what he's doing, what we're doing. I felt like he had a great offseason."

Double dipping – Demarcus Dobbs is one of three 49ers playing both offense and defense this summer.

Dobbs, heretofore a defensive end, has been learning tight end, a position he hasn't played since high school.

"It is tough," Dobbs said of the balance. "You have two playbooks that you have to learn. You flip-flop – one day defense, one day offense. So you constantly have to be in your books. But that's what we're here for."

Defensive coordinator Vic Fangio said the downside to the experiment is that every day Dobbs and the others spend on offense is one fewer on defense. "Does it affect his development at one position? Yes, it does," Fangio said. "There's no way around that. But in this case right now, it's better for the team and better for him and his chances of making the team."

Other players trying their hand on offense are defensive end Will Tukuafu and inside linebacker Michael Wilhoite. Both are learning fullback.

Et cetera – With Crabtree absent, Mario Manningham, Kyle Williams and A.J. Jenkins received extra practice repetitions and each made several nice plays.

• Colin Kaepernick continued to work as the team's No. 2 quarterback. He had a solid afternoon that included a nice throw across the middle to Davis.

• The pads go on today when the 49ers hold their first full-contact practice of the 2012 campaign.

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