Joe Mauer watched his closest friend in baseball suffer the debilitating effects of a concussion for more than a year. So when a foul tip off his catcher's mask inflicted a brain injury of his own, Mauer realized he doesn't want to emulate Justin Morneau.

Instead, he'll replace him.

In a decision tinged with irony, given the damage that concussions did to Morneau's career, Mauer and the Twins announced Monday that the St. Paul native will give up catching — the position that made him a six-time All-Star and the American League's Most Valuable Player in 2009. Mauer will take over for the departed Morneau as the team's full-time first baseman in 2014.

"It's one of the tougher decisions I've had to make, but also probably one of the easiest," said Mauer, after symptoms of his Aug. 19 concussion, which kept him out of the Twins' final 39 games, lingered into October. "I really tried to do everything I could to get back out on the field. But it wasn't safe and I wasn't able to do that."

Mauer, the only catcher ever to win three batting titles, insisted throughout September that he intended to return behind the plate once his head cleared. But as he battled persistent headaches, oversensitivity to light and noise and unexplained irritability, even two months after the seemingly innocuous and all-too-ordinary blow to his head, he said he realized the risk of recurrence was too great to ignore.

He consulted with Mayo Clinic experts and Twins team doctors. He explored sturdier masks and helmets. He sought advice from others including Morneau, a player whose MVP-level production never completely recovered from the head injury he suffered in July 2010. He noted how many catchers went on the disabled list because of concussions this season — seven, including teammate Ryan Doumit — and considered how utterly routine such head-jarring impacts are behind the plate. When doctors warned him that another concussion would likely last at least as long as this one, Mauer had heard enough.

"All it takes is one. That's one of the things I had to realize — if I said 'no, I'm catching,' all it would take is one foul tip in batting practice and I'm out again," said Mauer, who emphasized he is fully healthy and symptom-free now, and about to embark on a winter workout program. "I don't want to put myself in that position. I think it's the right decision not only for myself, but for my teammates and the organization."

Not to mention his family, too. In the past 12 months, Mauer has married and fathered twin daughters, another responsibility that gave him pause.

"I'm going to be a father and a husband a heck of a lot longer than a baseball player," the 30-year-old Minnesotan said. "If I didn't have them, it would be the same decision. But it's just a lot easier to make, knowing I have them" to think about.

The Twins now have to think about filling a position Mauer has occupied for a decade, though General Manager Terry Ryan sounded optimistic Monday that the current roster of catchers — Ryan Doumit, Chris Herrmann, Eric Fryer and especially rookie Josmil Pinto, who batted .342 in 21 games in September — would be able to handle the position. Signing a free-agent catcher is a possibility, Ryan said, but not an especially likely one.

"Most of our attention right now is on that pitcher's mound," he said.

Also less likely now: Morneau's return to Minnesota. Traded to Pittsburgh on Aug. 31, the four-time All-Star is a free agent, but "we've got a first baseman here," Ryan said, albeit one who has only 56 games of experience at first, only eight of them in 2013. "Hopefully he's going to be over there for 150 games."

Playing time is the biggest reason the Twins — who still owe Mauer $115 million over the next five seasons — so fully supported his decision. He has played more than 140 games only once in the past five seasons, and though his career batting average of .323 is one of the highest of all time for a catcher, he does the Twins little good when he's out of the lineup. A back injury kept him out for a month in 2009, leg ailments cost him roughly half of the 2011 season and he missed the final six weeks of this summer.

Even when he was "healthy," Mauer said, he often really wasn't.

"There have been many times I've [gone] up to the plate, [after] foul tips off my legs and shoulders, and I can't feel my hands," Mauer said, estimating he had suffered several other undiagnosed concussions from foul tips over the year. Mauer said Morneau, himself a catcher before switching to first base as a professional, told him: " 'You're going to be amazed at how much better you feel.' "

"I'm looking forward to that," Mauer said.

So is Ryan, who insisted the decision always rested with Mauer.

"I'm happy he has chosen to make the transition, but if he decided he wanted to catch, I'm not sure anybody was going to stand in his way," Ryan said. "We had a conversation in October. … Joe did some searching, talked to some people he had a lot of confidence in, and ultimately he got back to me and said he was willing to make the move. I think it's the right decision."