NASHVILLE, Tenn. — Starlin Castro called it “a tough moment,” but one that made him a better player.

The Yankees certainly hope so.

The Yankees’ newest addition and new second baseman up until last August was a career shortstop. But on Aug. 6 Cubs manager Joe Maddon pulled the plug, benching the struggling 25-year-old and shifting rookie Addison Russell from second to short. Five days later, Castro made his debut at second.

“Really frustrating,” Castro said in a conference call Wednesday afternoon. “But I didn’t want to be a bad teammate or be bad with my guys. Just continue with my head up . . . that moment made me grow up more.”

And, to the surprise of more than a few, an increase in production followed.

Castro, a three-time All-Star — most recently in 2014 — whose focus and maturity have been questioned by scouts and executives alike, excelled at the plate after the switch to second with a .353/.373/.588 slash line the rest of the way. Castro, who turns 26 in March, ended the season at .265/.296/.375 with 11 homers and 69 RBIs in 151 games.

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“I’ve always questioned his makeup a little bit but, to his credit, he played pretty well at second after being benched,” one rival executive said Wednesday. “He didn’t pout the way a lot of guys do in that situation. He put his head down and went to work. He showed me something I wasn’t sure was in there.”

The Yankees are confident Castro, signed by the Cubs in 2006 as a 16-year-old amateur free agent out of the Dominican Republic, has his best days ahead.

They like his athleticism and flexibility, confident he can serve as a backup to Didi Gregorius at short and Chase Headley at third. It was the reason the Yankees were willing to, for the moment, weaken their rotation depth by sending Adam Warren to the Cubs in the trade (Brendan Ryan will be the player to be named, which will become official after Thursday’s Rule 5 Draft).

“He’s a very talented guy,” said Jim Hendry, a top adviser of Yankees GM Brian Cashman who, as the Cubs GM in 2006, signed Castro. “History will tell you, the guys 26 to 33 have the chance to be your most productive. He’s an athletic kid, a first-class kid and I think he’ll fit in great.”

Castro, who counts Derek Jeter and Robinson Cano among his heroes and was mentored by former Yankee Alfonso Soriano in his early years with the Cubs, is looking forward to the change of scenery.

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“I feel really excited, I feel really happy,” he said. “That’s a really good opportunity for me.”