SAN FRANCISCO >> Erik Miller hadn’t thrown his sinker in about seven years when he took the mound at Oracle Park for his first offseason bullpen. Given how long the pitch had been dormant, he had no expectations for how the pitch would play.

He needed to throw just one to create shock and awe.

“I was like, ‘I don’t know if this is going to be great. We had the Trackman set up at Oracle. I threw the very first one. I looked back at the analysts. ... Their jaws both dropped,” Miller said. “Eyes wide open. Like, ‘Holy (expletive), that was legit. The movement on that was unreal for that pitch.’ As soon as I threw the first one, I was like, ‘We might be working with something here.’”

Miller, the lone lefty in the Giants’ bullpen, has brought back an old pitch for his sophomore season. It’s already giving left-handed hitters a new challenge. He’s only thrown a couple, but with its combination of velocity and movement, it’s already one of the best in the game.

Pitching coach J.P. Martinez approached Miller about playing around with a sinker while playing catch during the offseason. Martinez saw Miller artificially raising his arm slot last season to get additional vertical movement on his four-seam fastball, so tossing around the sinker would help Miller get behind his four-seamer more and generate additional vertical movement. The unintended result was another way to neutralize lefties.

On Monday, Miller struck out Yordan Alvarez, one of baseball’s best hitters, with a sinker that clocked in at 99 mph and generated nearly 20 inches of horizontal movement. Miller is currently averaging 18.0 inches of horizontal break on his sinker; for context, the Minnesota Twins’ Michael Tonkin generated the most horizontal break with his sinker at 18.8 inches. The sinker generates so much movement that Miller aims his sights at the right-handed batter’s box.

“We wanted something that could really dominate lefties, and it felt like that was the right pitch,” Martinez said. “Anytime you get a same-side sinker that moves that much and it’s that hard, it’s going to be a good pitch.”

The sinker enables Miller to become more of an east-west pitcher who’s capable of covering both sides of the plate. Miller’s sinker and changeup, another excellent offering in its own right, move into left-handed hitters. The slider, by contrast, moves away from lefties. The task of hitting Miller is all the more difficult because Miller’s sinker “mirrors” his slider, meaning both pitches are nearly indistinguishable coming towards the plate until they inevitably break one way or the other. He’s only thrown two sliders this year over his four outings, but that’s been due more to matchups. If Miller wants to go upstairs, he can call upon the four-seamer.

“Last year, I felt it could keyhole me a lot where lefties knew I was going four-seams away, sliders away — everything was going to be away from them,” Miller said. “Now, I have something that can get in on their hands and force them to honor the inside part of the plate.”