Joe Mauer turned 33 on Tuesday.

Hard to believe, isn’t it? He debuted with the Twins 12 years ago this month, a fresh-faced son of St. Paul with a smooth swing and unlimited expectations. No current Twin has been with the organization longer, and Mauer is the last of the four original occupants of the corner locker stalls in the Target Field home clubhouse still active in baseball. 

His career falls into two distinct eras: Golden from 2004 through 2013, when he won three batting titles and an American League MVP award as one of the best-hitting catchers in baseball history; and brass after Aug. 19, 2013, the day he suffered the concussion in a makeup game against the Mets that prompted his move to first base. 

Post-concussion, Mauer’s production plummeted. His average fell below .300 in back-to-back seasons while his strikeouts, which have been trending upward since 2012, soared to a career-high112 last year. That further inflamed the subset of frustrated Twins fans disgusted with Mauer and his $23 million annual salary.

The low point came last July 30, when Seattle manager Lloyd McClendon ordered Aaron Hicks intentionally walked to get to Mauer, a startling show of disrespect to a six-time All-Star. Though Mauer singled in a run, the message was clear: Mauer’s days as a dangerous hitter were over.

Or are they? 

Monday night, in the sixth inning of a rain-shorted game with Milwaukee, Mauer stepped to the plate at Target Field with Brian Dozier at first, one out and the Twins leading 6-4. Facing former teammate Blaine Boyer, Mauer took the first three pitches – a strike, a ball, then another strike. He fouled off a slider, took a fastball off the plate for ball two, then drilled another fastball down the left-field line for a run-scoring double. 

In a way, this was a classic Young Joe at-bat – patient and productive, with a big two-strike payoff. The double gave Mauer a nine-game hitting streak, a .362 batting average and 1,714 career hits, fifth-best in Twins history and one more than beloved Hall of Famer Harmon Killebrew. 

“Any time you’re mentioned with Harmon, you’re doing something really good,” Mauer said. “That’s really special.” 

So is this: After two years of concussion-related vision problems, Mauer may have regained the keen strike zone judgment that Baseball America rated the game’s best in 2012 and second-best in 2013.

It’s a small sample, three weeks into the season, but Mauer leads the American League in on-base percentage (.472) and ranks among the top ten in batting (.339). Mauer is taking fewer bad swings, making contact more often, and hitting more line drives than he has since the concussion.

Data compiled by the statistical service Baseball Info Solutions through Wednesday’s games show Mauer making contact on 92.6 percent of all swings, an eight percentage-point improvement over last year. (He exceeded 90 percent in 2008 and ’10 and came close in 2009, his MVP year.) In addition, 36.7 percent of balls Mauer puts in play are classified as hard hit, a rate he hasn’t produced at since 2013, right before the concussion (37.4).

Mauer is also chasing about 10 percent fewer pitches out of the strike zone than last year. PITCHF/X, Major League Baseball’s pitch-tracking service, shows Mauer swinging at 33.9 percent of all pitches, down from a career-high 41.3 percent in 2015. 

The gist: Mauer is back to being more selective. For a club that started 0-9, that may be the most encouraging news in the early going.

“What you look for is results,” said Twins manager Paul Molitor, the Hall of Famer and fellow St. Paul product. “Some of the calmness he seems to be having through the course of his at-bats…it’s only 45 at-bats, or whatever it might be. But he’s getting his walks, and getting big hits against lefties as well as righties.

“People try to look at what he doesn’t do as opposed to what he can do, and so far it’s been good.”

Before the concussion, Mauer’s plate discipline made him one of baseball’s better two-strike hitters, and that may be trending back as well. Through Wednesday, with two strikes Mauer was hitting .370 (10-for-27) with eight walks and five strikeouts. Last year’s MLB average with two strikes: .177, according to baseball-reference.com. On 0-2 counts alone, Mauer is 5-for-6 without a strikeout.

“The big difference right now — and it’s way too early to put this into a pattern — is he’s putting the ball in play,” said Twins general manager Terry Ryan. “He’s not striking out. When you look at that raw stat page, he’s walking more than he’s striking out.

“He’s off to a nice start. It’s April and we’d like to withhold judgment before we get too carried away, but he’s got things going in his direction.” 

It took Mauer two years to reveal what some of us suspected: Lingering post-concussion symptoms left him with occasional blurred vision, hindering his ability to pick up the ball’s rotation. Recognizing a pitch as a fastball, slider or a curve is crucial to hitting, and the last two years Mauer often flailed at pitches he usually took before. In case you missed it, Brian Murphy of the St. Paul Pioneer Press broke the story just before spring training.  

Now, it wasn’t all eyesight. More than any other Twin, Mauer struggled adjusting to a slightly lower strike zone. And a scout who monitors the Twins said younger umpires rarely gave Mauer the benefit of the doubt on borderline pitches, a courtesy veteran umps bestow on a handful of respected players.

It also helps that Mauer is healthier overall than any time since 2012, the season after he received lubricating injections in his troublesome left knee. Mauer injured that knee the first week of his rookie season; subsequent surgery removed 80 percent of the cartilage, he said.

“I feel good all over, my whole body,” Mauer said. “It seems like I’m seeing the ball better, having better at-bats, not chasing pitches that I have been the last couple of seasons maybe.”

Mauer also appears a bit more nimble around first base. Last Friday, Mauer threw out a runner at third from short right after right fielder Miguel Sano and second baseman Eduardo Nunez collided chasing a pop fly. That revived questions about why the Twins moved the hulking Sano, who reportedly weighs close to 280 pounds, from third base to right field instead of putting him at first and shifting Mauer to right. Mauer played one game in right field in 2011.

Ryan said the Twins considered that, but decided against asking two players learn new positions on the same side of the field.

 “Sano’s got a way better arm than Joe,” Ryan said. “Joe’s got plenty of arm to play right field, but Sano’s just got a powerful arm.” And, Ryan added, “Joe’s done a nice job over at first. He saved a couple of runs already.”