TAMPA, Fla. — Seranthony Domínguez entered the game to face one of the best hitters alive.

José Ramírez, a six-time All-Star, stepped to the plate for the Cleveland Guardians against the Orioles’ reliever during a game in mid-April.

Ramírez is one of those hitters that is so good — he’s posted an OPS north of .800 in every season since 2016 — that there’s almost nothing that can make him look bad. He’ll get out, of course, and occasionally strike out, but he almost always does so with the grace of a future Hall of Famer.

But then Domínguez threw a pitch that baffled Ramírez — and everyone else who noticed it.

“Oh damn,” Orioles pitching coach Drew French remembers thinking while watching from the home dugout at Camden Yards.

The splitter from Domínguez was so impressive and so difficult to hit that Ramírez came nowhere close to making contact before letting the bat slip out of his hands.

As the bat rolled on the ground near the first base dugout, Ramírez looked toward the videoboard in bemusement, almost as if he was asking himself where Domínguez found a pitch like that.

“When you see him swing like that, that pitch has got to be really good to make him look the way he look,” Domínguez said.

Two months later, his splitter — a pitch he learned this offseason — is perhaps the best in baseball. And the offering has thus far transformed the hard-throwing right-hander into a much more reliable and dominant reliever.

“I knew if it worked, it was something that could help my career a lot,” he said. “I feel like right now I have better stuff than ever before.”

Domínguez upped his splitter usage in late May and has since been one of the best bullpen arms in baseball. Since May 26, the 30-year-old has pitched 11 2/3 scoreless innings with a 0.771 WHIP and a whopping 42.9% strikeout rate. Over that span, he’s sixth among qualified relievers in wins above replacement by FanGraphs’ estimation and seventh in strikeout rate.

A direct line can be drawn between Domínguez throwing the splitter — an offering that features the pitcher’s ring and middle fingers much farther apart than normal — more and his recent dominance. Opposing hitters are batting a measly .095 off it and whiffing 58.8% of the time, entering Thursday.

According to Baseball Savant, it is the best splitter in baseball on a per-pitch basis — yes, even better than closer Félix Bautista’s, which ranks third — and 23rd among all offerings from every MLB pitcher among those thrown at least 50 times.

“There’s a lot of confidence there right now,” interim manager Tony Mansolino said. “He wants the ball. We want to give him the ball. We’re really excited with where he’s at right now.”

After the Orioles acquired Domínguez at last year’s trade deadline, he quickly became their closer after Craig Kimbrel’s implosion. It was a role Domínguez was familiar with dating to his rookie year with the Philadelphia Phillies, for whom he dominated in the postseason in 2022 and 2023. With Félix Bautista back this season, Domínguez is one of the Orioles’ setup men.

For most of his seven-year career, though, Domínguez has pitched through a flaw that’s made his life as a reliever more difficult.

Like many righty relievers, Domínguez struggles against left-handed batters. In his career, righties have hit only .185 with a .563 OPS off Domínguez — elite numbers that made him one of the game’s best right-on-right relievers. But lefties have fared much better with a .245 average and .754 OPS.

The cause for this — aside from the macro platoon advantage opposite-handed hitters have — was the fact that Domínguez’s main offspeed pitch is a slider (or the past two years more of a sweeper). The pitch is much more effective against righties, since it moves away from the batter, than against lefties. From 2022 through 2024, Domínguez tested out a changeup, throwing it between 4% to 13% of the time, but it wasn’t an effective pitch. Domínguez is a supinator — a pitching term about a pitcher’s wrist/hand position at his release point that in layman’s terms means he’s able to spin breaking balls well — so a changeup is difficult for him. It felt uncomfortable in his hand, reducing his confidence and forcing him to “locate it too much” rather than just throw it.

This offseason, Domínguez set out to find a pitch that can get whiffs against lefties. He worked out with and learned from Héctor Neris, a 12-year veteran whose nasty splitter made him one of MLB’s best relievers from 2016 to 2023, and former big league pitcher Joel Peralta. The splitter gives Domínguez a pitch that drops — in his case, it falls off the table — while also moving horizontally away from lefties.

He showed up to spring training to show French and the other Orioles pitching coaches his new toy.

“We just loved it,” French said.

But Domínguez struggled with his command throughout spring training, and that became a primary focus. He then got on track in April and was dominant early on, so the splitter remained on the “back burner,” French said. Domínguez, a one-inning reliever, has five pitches, making it difficult to make drastic changes to his pitch mix. The two he threw to Ramírez in that at-bat in mid-April were only the third and fourth ones he’d thrown all season. He threw only two more through May 14.

Domínguez hit a speed bump in May, though, allowing 12 runs in a span of 9 2/3 innings with a lot of that damage coming from left-handed hitters. That’s when he and the Orioles decided to truly incorporate the splitter into his pitch mix.

“I feel more comfortable,” Domínguez said of facing lefties. “The more that I throw it now, the more comfortable I feel with it.”

Mansolino has since used Domínguez as a platoon-neutral reliever, trusting him against both lefties and righties. Domínguez was previously used mostly against pockets of right-handed hitters.

Have a news tip? Contact Jacob Calvin Meyer at jameyer@baltsun.com, 410-332-6200 and x.com/JCalvinMeyer.