Sean Doolittle dropped off-speed stuff on the Astros on Saturday. (Jeff Roberson/Associated Press)

WEST PALM BEACH, Florida — Sean Doolittle threw two sliders and a couple change-ups Saturday afternoon, choices that wouldn’t earn much notice with most major league pitchers, but constitutes a significant development for the Nationals’ closer.

Doolittle rarely throws sliders. He seldom throws his change-up. In fact, over the last five seasons, only three relievers have thrown a greater percentage of fastballs than he has — Orioles closer Zach Britton, Dodgers closer Kenley Jansen, and Rockies lefty Jake McGee. Britton and Jansen have accumulated the eighth-most and second-most saves in baseball during that half-decade. Closers can thrive with just a fastball. This offseason, and now this spring, Doolittle renewed a career-long, concerted effort to add legitimate off-speed pitches to his mix.

““It’s definitely been a point of emphasis,” Doolittle said. “I think in the two outings I’ve had, I’ve thrown more sliders to righties than I think I have in my whole career. … The change-up has continued to progress from where it was last year; that’s a pitch I felt comfortable with over the second half of last season.”

Britton built his career on a devastating sinking fastball. Jansen relies on a heavy cutter. Doolittle relies on pure heat, located with pinpoint accuracy, delivered with enough deception to add a few perceived miles per hour to every pitch he delivers.

As with Britton and Jansen, Doolittle enters every game with a predictable game plan: set hitters up with fastballs they can’t square, put them away with fastballs up they can’t reach. He seizes on hitters’ tendencies to overswing late in games, to sit on fastballs and try to hit them a mile. But because he doesn’t have Britton’s sink or Jansen’s jam-you-up cut, if he misses, movement doesn’t save him. As Dusty Baker always used to say when discussing Doolittle’s weaknesses, “beware the fastball-hitting right-hander.” Emphasizing the slider should help Doolittle combat just that type of late-game menace.

Doolittle has always felt comfortable throwing his slider to left-handed hitters. It moves away from them. He can get swings and misses out of the zone. As long as he buries it low or starts it on the plate and runs it off it, no left-handed hitter will be able to do much damage against it. But against right-handers, Doolittle never gained the same confidence in the pitch. He often threw that slider toward a right-handed hitter’s back foot, or ran it down into the dirt, changing eye level but never forcing a right-hander to give the pitch much consideration. Saturday, the two sliders he threw to right-handed hitters carried more purpose. Marwin Gonzalez popped one of them up; Carlos Correa watched his, then struck out a few pitches later.

Doolittle polled the locker room about his slider. He asked his teammates and coaches how he should throw it. He tinkered with grips over the first few weeks of spring and settled on a cut fastball grip that would give him more of a power slider to bear in on righties. Then he abandoned that grip in favor of a more traditional breaking-ball grip, which he now combines with an attacking mind-set he honed while tinkering physically. The result, on display Saturday, is a low-80s slider with significant break that Doolittle feels he can throw to righties with the same attacking intentions he would a fastball.

“Where before I was thinking: ‘Where can I put [the slider] where I won’t get hurt?’ … Now when he puts it down, I’m more willing to attack the strike zone with it,” Doolittle said. “I want them to swing at it, because I think I can get good quality contact [for me] maybe early in the count.”

Doolittle threw 16 pitches in his scoreless inning Saturday, which ended with that strikeout of Correa in which he used both the slider and change to keep the Astros’ superstar off-balance. But the left-hander’s vision for throwing more sliders and change-ups doesn’t necessarily include more strikeouts of right-handed hitters. Instead, he dreams it will allow him to orchestrate fewer strikeouts, thereby increasing his efficiency.

“Maybe I don’t have to throw two or three fastballs to set up the high fastball for the potential strikeout. Maybe I can get a groundball on a change-up in the second pitch of an at-bat,” Doolittle said. “Yeah, I’ve had some injury history, but maybe over the course of the season, if I can keep my pitch count to 12, 15 per inning, that goes a long way.”

The 31-year-old missed time with shoulder trouble last year and has a history of similar issues forcing him to the disabled list. Manger Dave Martinez has Ryan Madson and Brandon Kintzler to close on days when Doolittle needs a break. The Nationals probably don’t need to overwork him early in the season. Still, weak contact early in counts could reduce the number of pitches Doolittle has to throw and could reduce the number of high-stress fastballs he needs to throw to big right-handed hitters in key spots.

All of this remains theoretical. Doolittle cannot afford to combine an attack-first mind-set with a half-ready breaking ball during the fire of regular season ninth innings. He rarely has margin for error. So each time he lands a few sliders or executes a few change-ups this spring, it represents progress. A few more weeks of good results, and Doolittle could enter the regular season with a broader arsenal than before. A few struggles, and he probably won’t have time to hone those pitches during the regular season, which could mean reverting to that fastball — which hasn’t exactly failed him yet.

Still, the whole league knows Doolittle’s soft spot — “Beware the fastball-hitting righty.” Doolittle’s goal this spring is to establish his secondary stuff enough to make right-handers wary of a slider-tossing lefty.

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