MANKATO – Vikings rookie center Pat Elflein has a few seconds to boil down hours of playbook study. The hand of 329-pound Linval Joseph is stamped in the dirt across the line. An $18 million quarterback waits on him.

Who's the middle linebacker? What protection adjustment is needed based on the play call and one of the defense's frenzied looks? Making the right calls — and loudly enough — will help decide whether or not the third-round pick can compete with incumbent Nick Easton for the center job, which is a key opening remaining in the retooled Vikings offensive line.

There's no time to waste, according to offensive line coach Tony Sparano.

"You really want to get that body in as soon as possible," Sparano said. "I think the longer a center position competition goes, as opposed to maybe some other competitions within the line, you know, that can cause confusion.

"There's no real timetable," he added. "We just know it's got to happen fast."

The clock is ticking. Elflein, swapping first-team series with Easton during Saturday's first padded practice of training camp, makes a late change. Turning his head left and right, he shouts the new call.

Pat Elflein (65) won the Rimington Trophy as the nation’s top center last year at Ohio State, but that’s not enough to earn him a starting job with the Vikings.

"Say it so everybody can hear it," said Joe Berger, the right guard and former starting center. "And not just kind of mumble it out there. So I know sometimes my experience is as a center, if you're not sure if you've got the right call or not, you kind of just mumble it out. And then nobody hears you and it doesn't really matter that you did say it."

Quick and clear mental processing is critical at the center position, where the Vikings have enjoyed a lifetime's worth of studs from Mick Tingelhoff in the 1960s and '70s to Matt Birk in the 2000s. Elflein is a quick study by many accounts, but the former right guard is only in his second full year playing center. And the 23-year-old Ohio State product is still gaining confidence with each snap. He will question his own calls at times.

"Coach Sparano calls it chasing ghosts," Elflein said. "Where when you're trying to make the correct call and there's a lot going on, really just kind of overthinking it, so you've got to know to stay true to your rules."

That's where Easton, the third-year center out of Harvard, has a leg up in the competition. Easton has five career starts under his belt, all coming in the final five games of last season. His debut came on a Thursday night game against the Cowboys, when Easton took some lumps that Elflein is also bound to see.

"[Easton] played well, but there were some things he saw for the first time," Sparano said. "You know at the center position, you can't have a tiny scope. Your scope has to be wide open, you have to see the entire field."

Physically, they are listed the same, 6-3 and 303 pounds, though that might be a generous height for both. They are each what the Vikings are looking for in a modern center: a sturdy base, quick brain and brawler's mentality. Vikings General Manager Rick Spielman noted Elflein's fiery responses when he made choreographed jabs at him during predraft interviews.

Easton draws the "smart" and "tough" labels from Sparano. What will separate either is how well each holds up against Joseph, the Vikings' Pro Bowl nose tackle, in practice. On Saturday, Easton locked Joseph into a stalemate with a successful shuffle during 1-on-1 drills. Joseph was later too much for Elflein in the same session.

"I mean, that's the bottom line," Sparano said. "There's no better test."

The Vikings don't always produce quality offensive lines, but they have almost always had a reliable center. The hunt for the next continues after the latest stalwart, John Sullivan, suffered a herniated disk in his back and missed the 2015 season. Berger admirably took over and earned three All-Pro votes that year before injuries last year forced him to right guard, where he remains this summer.

Center might be the last unsettled spot for this offensive line. Much of the focus is rightfully paid to both tackle spots, but each side of the line will get its direction from the center.

Coach Mike Zimmer doesn't want this to be a prolonged process like last summer, when the Vikings rotated players at center and right tackle during preseason games. This time, Zimmer wants to peg a starting five and leave it alone.

"Sooner the better, obviously," Zimmer said. "I don't want to go through everything we went through a year ago."