Boston Found a Top Reliever in the Yankees System. Blame Instagram.

The Jeep Wrangler with the Yankees tire cover became a familiar sight at the Central Alabama Baseball Academy in 2020.

The vehicle belonged to Garrett Whitlock, who received the navy cover with the interlocking “NY” insignia as a gift after the Yankees drafted him in the 18th round in 2017. Whitlock drove the Jeep to his job as one of the academy’s pitching coaches, a paid gig he picked up while recovering from Tommy John surgery amid a minor league season canceled because of the coronavirus pandemic. He frequented the travel program’s facilities, often throwing bullpens as he restored his arm’s strength.

So when the Red Sox scooped up the right-hander with the fourth pick in the Rule 5 Draft on Dec. 10, 2020, those at the academy instantly noticed the naked tire when he arrived later that day.

“It was pretty funny,” said the academy’s founder, and former minor league catcher, Kennon McArthur, who employed Whitlock for about six months. “Getting picked up by the rival.”

Whitlock was a revelation for Boston in 2021 after the Yankees opted to protect other pitchers on their 40-man roster. The 25-year-old recorded a 1.96 E.R.A. and struck out 27.2 percent of the batters he faced in the regular season. He threw three and a third scoreless, high-leverage innings in Boston’s division series against the Tampa Bay Rays and contributed two scoreless innings in the team’s Game 2 win in the American League Championship Series on Saturday. In the biggest gut punch to the Yankees, however, he was on the mound, working around a solo homer to close out Boston’s wild-card game win over his former club.

Whitlock hadn’t pitched above Class AA before this season, yet he has stepped up as the most valuable reliever for a team with championship aspirations. Just don’t tell him that.

“I’m still just trying to earn my spot on the team,” Whitlock said of his lofty status despite his limited résumé.

Recently Whitlock said he had joked with Chris Messina, Boston’s strength coach, about how he was officially a member of the team now that the regular season had been completed, thus finishing off the terms of the Rule 5 draft, in which a player has to stick with the team that chooses him all year or be returned to his original club. All the Yankees received for the young pitcher was $100,000.

“I joked, ‘You’re stuck with me now,’” Whitlock said.

While Whitlock comes off as unassuming, Manager Alex Cora immediately saw promise in the young pitcher and said the decision to keep Whitlock around was easy back in spring training.

“We saw him throwing a bullpen and I was like, ‘This kid’s making the team,’” Cora said. “He’s A-plus. He’s great. Talent-wise, you saw it throughout the season.”

The Sox knew about Whitlock’s successful rehab from elbow surgery thanks to social media. He had documented his recovery on Instagram, sharing progressively more intense practice sessions while clad in Yankees apparel.

“Instagram gets a shout out,” Cora said after Whitlock closed out Game 4 of their division series against the Chicago White Sox with two shutout innings. “I’m glad that some of the scouts have Instagram and saw him throwing a bullpen.”

Whitlock said he “never” imagined he would be in such a high-leverage role for the Red Sox.

Before Game 4 of the division series, he recounted the day he officially made the Red Sox. He was in the weight room at Boston’s spring training complex when Cora told him they needed to talk. “This is going to be one of two things,” Whitlock naturally thought. He and Cora joined a Red Sox contingent that included Chaim Bloom, the team’s chief baseball officer, along with Dave Bush, the pitching coach, Jason Varitek, a game-planning coordinator, and Kevin Walker, the bullpen coach.

“Hey, have you got any plans for April 1?” Whitlock remembers Bloom asking in reference to opening day. “We’d love to have you out there.”

Whitlock described making the team as the most memorable moment from a season full of special ones. But it wasn’t until months later that he truly believed he belonged in the majors.

It was Sept. 12, and he had just surrendered a walk-off home run to Leury Garcia, a utility player for the White Sox. The latest stumble in a rough start to the month left Whitlock sitting alone in the visitor’s clubhouse bathroom at Guaranteed Rate Field. “I was down on myself,” he recalled.

Then Kiké Hernandez walked in, ready with a pep talk. Hernandez reminded Whitlock that he had been a pillar of Boston’s bullpen. He would remain one.

“He was just like: ‘Hey, man, you’ve been huge for us all year. You’re going to continue to be huge for us,’” Whitlock said. “Once he said that, that gave me a lot of confidence.”

Lately, Whitlock is trying to “soak up everything.” It has been a year of considerable change, frequent firsts and heightened expectations. “You never know if this will happen again,” he said of his surreal season. As McArthur framed it, Whitlock went from “being an injured minor league player to a stud in the big leagues.” Whitlock doesn’t plan on losing sight of that.

“If I ever have a day where I’m just like, ‘Oh, it’s another day,’ that’s the day you come and take me out,” he said. “I never want to take a day for granted ever again.”