Joe Dillon introduced a scientific approach to batting instruction to the Washington Nationals in 2018, prompting lead hitting coach Kevin Long to laud him as “the best assistant in baseball.”

Not even two years later, the Phillies believe Dillon is the coach to unlock an offense that underachieved for much of last season.

Dillon was hired Thursday as the Phillies’ hitting coach, the team announced. He will join new manager Joe Girardi’s staff and be the full-time successor to John Mallee, who was let go in August and replaced on an interim basis by former manager/hitting savant Charlie Manuel.

“I was impressed with Joe’s knowledge of swing mechanics and his ideas on how you combat today’s power pitchers,” Girardi said in a statement released by the Phillies. “He has great drills to use to prepare hitters for velocity.”

Girardi’s initial familiarity with Dillon stemmed from his relationship with Long, his hitting coach for seven seasons with the New York Yankees. Long’s endorsement seems to have carried considerable weight, too, as Girardi credited Dillon with keeping the Nationals’ hitters prepared during a six-day layoff before the World Series.

The Nationals were never going to let Long bolt for an equivalent job with a division rival. Hiring Long’s trusted right-hand man -- “I’ve got the best assistant in baseball,” Long told the Washington Post in 2018-- appears to have represented the next-best thing for Girardi.

A .263 career hitter over parts of four major-league seasons as a utility player for three teams, Dillon is known for studying the cognitive tendencies of his hitters, such as their respective rates of making contact within the strike zone and chasing pitches outside the zone, and tailoring drills to improve their respective skills.

Dillon, 44, espouses launch angle and other popular tenets of contemporary hitting instruction. But while Mallee preached a universal “selective-aggressive” approach, Dillon seems to take a more individualized tack and doesn’t force his methods on any hitter.

According to a Washington Post article in spring training last year, Nationals shortstop Trea Turner and first baseman Ryan Zimmerman were Dillon disciples who took advantage of his cognitive-based drills. Bryce Harper, however, notably preferred to stick to his own routine.

The article also highlighted Dillon’s novel approach to batting practice, which included using machines to throw specific pitches at different planes and angles to better simulate game conditions. Unlike in batting practice, when hitters swing at almost everything, game action requires that they train their eye to make split-second choices about pitch selection and location.

Rhys Hoskins will be Dillon’s biggest initial pet project with the Phillies. The slugging first baseman endured a miserable second half of the season, batting .180 with a .318 on-base percentage, .361 slugging percentage, and nine home runs in 313 plate appearances after the All-Star break.

As a team, the Phillies were expected to slug their way to playoff contention. Instead, they ranked eighth in the 15-team National League in runs (774), ninth in hits (1,369) and slugging (.427), and 11th in homers (215) and on-base percentage (.319).

Hoskins wasn’t the lone underachiever. Jean Segura, for instance, slashed .280/.323/.420, an across-the-board drop-off from his previous three seasons with Seattle and Arizona (.308/.353/.459).

Before hiring Dillon, the Phillies also met with Matt Stairs, the 19-year big-league veteran whose tide-turning pinch-hit home run at Dodger Stadium in Game 4 of the 2008 NL Championship Series made him immensely popular among Phillies fans. Stairs also served as the club’s hitting coach in 2017, and therefore is familiar with many Phillies hitters.

Ultimately, though, the Phillies went with Dillon, the closest thing to Long that Girardi was going to find.