Didi Gregorius of the Yankees follows through on a fifth-inning...

Didi Gregorius of the Yankees follows through on a fifth-inning two-run home run against the Twins at Yankee Stadium on Tuesday. Credit: Jim McIsaac

When the Yankees acquired Didi Gregorius from the Diamondbacks on Dec. 5, 2014, general manager Brian Cashman thought he was getting a young player with significant upside.

But no one could have predicted this.

Now in his fourth season as the Yankees’ shortstop, Gregorius has improved specific facets of his offensive game every season. It’s why he seems to be bursting on to the scene this year as one of the best all-around players in baseball, with power and a newfound ability to draw walks along with being a Gold Glove-level shortstop.

That’s not who Gregorius was when he replaced Derek Jeter in the Yankees’ lineup on Opening Day 2015. Gregorius hit ninth that day, and did again on Opening Day 2016.

After starting the year on the disabled list in 2017, Gregorius hit sixth when his season opened April 28. By the postseason, he was the Yankees’ third or fourth hitter.

Still, after the acquisition of Giancarlo Stanton, new manager Aaron Boone batted Gregorius sixth in the 2018 opener on March 29. As March turned to April and Stanton and Gary Sanchez struggled, Gregorius thrived. He moved to cleanup and then to third as a lefthanded wedge between Aaron Judge and Stanton.

Gregorius’ stats entering Saturday night are staggering. He was hitting .368 with 10 home runs (the first nine at Yankee Stadium, the 10th a go-ahead homer in the 10th inning of the Yankees’ 4-3 win over the Angels on Friday night). He was tied for the major-league lead in homers with Mike Trout.

Going into Saturday, Gregorius led the majors in RBIs (30), batting average, slugging percentage (.828), OPS (1.286) and WAR (2.4, FanGraphs version). He had homered in five of the last six games.

Gregorius, who never has been an All-Star, has emerged at age 28. Like most so-called “overnight successes,” he has spent thousands of hours working to become the player he has been this season. Here’s how he’s done it since coming to the Bronx in a three-way deal in which the Yankees sent righthander Shane Greene to Detroit:

2014-2015: LEARNING TO HIT LEFTIES

Gregorius hit .137 against lefthanded pitching with Arizona in 2014. It was a weakness that threatened his ability to be an everyday player, so he worked at it tirelessly.

“What I learned is just stay in there closer, keep the front shoulder closer, foot down early, and try to recognize the ball as fast as you can,” Gregorius told YESNetwork.com last year.

In 2015, Gregorius improved to .247 vs. lefties. In 2016, he hit an astounding .324. Last season, he was back to .264. After Friday night’s game, he had a .400/.483/.720 slash line with two homers in 25 at-bats against lefthanders.

It is a weakness no more.

2015-2016: POWER SWITCH ON

Gregorius was not acquired to be a home run hitter, but he did appear to have extra-base hit potential. Still, his career high in home runs coming into 2016 was the nine he hit in his first Yankees season in 2015. In 2014 with Arizona, Gregorius had a slugging percentage of .363. The next year with the Yankees, it was .370.

The big leap came in 2016, when Gregorius had a slugging percentage of .447 along with 32 doubles, 20 home runs and 70 RBIs, all career highs. The added home run power wasn’t a Yankee Stadium fluke, as Gregorius hit 11 homers at home and nine on the road.

“I’m not a home run hitter,” he said this past week. “I’m trying to hit line drives all over the place. If they go out, they go out.”

Hold that thought.

2016-2017: MISS A MONTH? NO WORRIES

Despite missing the first month with a shoulder injury suffered in the World Baseball Classic, Gregorius still set full-season career highs in batting average (.287), home runs (25), RBIs (87), slugging percentage (.478) and OPS (.796). He appeared in only 136 games after averaging 154 in his first two Yankees seasons. Gregorius also picked up his first MVP love — one eighth-place vote.

Hold that thought, too.

2017-2018: EARLY MVP CANDIDATE

Even with Judge and Stanton in the lineup, Gregorius has been the Yankees’ best hitter.

Gregorius has learned to control the strike zone. His career high in walks is the 37 he had in 404 plate appearances with Arizona in 2013. Five were intentional, a function of batting eighth in a National League lineup.

With the Yankees, Gregorius’ previous full-season walk totals were 33, 19 and 25. Entering Saturday night, he had 17 in 109 plate appearances in 25 games.

“To see him really kind of controlling the strike zone has been, I think, his next step in continuing along to becoming a really, really good player,” Aaron Boone said. “I think in a kind of understated way he really understands the league. He understands what pitchers are trying to do to him. I think he’s really good at developing a plan and I think he’s just grown year by year into a guy that’s been able to continue to make adjustments coupled with the fact that he’s really talented, too.”

Gregorius called it “sticking to a game plan. Just see how the guy pitches you and try to stick to that. If he’s trying to pitch around you, just take a walk, which everybody knows I don’t walk that much. So I’m learning to try to lay off those pitches and try to get on base for the next guy.”

2018-ON: NOW WHAT?

Gregorius, who is making $8.25 million, is eligible for arbitration after the season and can become a free agent after the 2019 season.

Boone was asked if Gregorius is a better player than he had anticipated.

“Yes,” he said. “Because he’s gotten better and he’s just taken another step. But we’ve seen it happen now for the last few years. I’ve actually followed his career pretty closely from afar, I guess you’d say. Living in Arizona, I knew when he went from the Reds to Arizona [in 2012]. I always thought he could be a really good player, but to see him come here and get better and better and better each and every year, and now I think he’s taken another step this year.”

What’s next for Gregorius? An All-Star selection would be nice, but the American League has a lot of top shortstops, including Baltimore’s Manny Machado, Houston’s Carlos Correa, Cleveland’s Francisco Lindor, Boston’s injured Xander Boegarts and the Angels’ Andrelton Simmons.

Thus far, Gregorius has been better than all of them.

“It’s pretty cool just to see that as a teammate,” Judge said. “All the hard work he’s put in over the years. I’m excited for the rest of the year.”

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