Jordan Zimmermann has a change-up. That sounds innocent enough. But in baseball, that’s like saying a gorilla just learned how to use a machine gun. Every pitcher who lacks a change-up is dying to get one. It makes every other pitch look better by contrast. But there may not be a hard-throwing hurler in the whole sport of whom it has been said more often, “How good would he be with a change-up?” Now, it looks like we’re about to find out. On Monday, the normally stoic Zimmermann looked giddy after he had retired 18 Tigers in a row and baffled many of them with his new change-up. “I had all four pitches working,” the Washington Nationals’ right-hander said. “It’s hard to come by those days. They don’t come by often. You feel like you can’t do anything wrong. I threw a lot of good change-ups that were falling below the zone.” Some of us have never seen him smile, much less grin, look sheepish, make quips and then disappear saying, “Let me sleep on this.” Sweet dreams, indeed. “The change is that equalizer pitch,” shortstop Ian Desmond said after watching Zimmermann hang a meek 0 for 12 on Prince Fielder, Miguel Cabrera and Victor Martinez — three of the best sluggers in baseball — as well as Detroit standouts Torii Hunter, Omar Infante and Alex Avila. Until that game, Zimmermann might have been the Nats’ biggest worry. Ten days earlier, he gave up eight runs against his Cardinals nemeses and said he had a “dead arm.” But he predicted he would bounce right back, which he did with a solid outing. But few were prepared for Monday. Zimmermann has talked about his new change-up all spring. But his pitching buddies have teased him that it’s just “a February change-up,” that will disappear in the regular season as soon as somebody lights one up with a 450-foot charge. The new pitch likely won’t go back in the ball bag now.