Garrett Whitlock is officially returning to his very successful rookie roots.

“Let’s go back to the bullpen, baby!” the Red Sox right-hander said at Fenway Fest on Saturday.

Whitlock owns a 3.39 career ERA over 103 regular-season games, including 23 starts, 24 games finished, and nine saves. As a reliever, however, he’s pitched to a 2.65 ERA with 150 strikeouts over 132.2 innings, compared to a 4.29 ERA and 102 strikeouts over 109 innings as a starter. He’s proven adept at handling high-stress situations, holding opposing batters to a .208 average and .613 OPS in late-and-close situations (seventh inning or later with the opposing team tied, ahead by one, or with the tying run on deck). He’s pitched best in high-leverage situations, with lineups averaging a meager .197 and .593 OPS against him.

“Obviously, I still have the repertoire and everything to start and if they need me to do that, I’ll do that,” Whitlock said. “But just talking to (manager Alex Cora) and everything, it’s comfortable (in the bullpen) and it’s where I’ve had success and everything, so it’s what we think is going to help give the team the best chance to win.”

Whitlock’s last season working solely as a reliever and the Red Sox’s most recent postseason run were one and the same. As a rookie in 2021 he pitched to a 1.96 ERA over 46 regular-season appearances, including 11 games finished, and racked up the second-most strikeouts in the bullpen (81). He ranked in the 85th MLB percentile or better in expected on-base (xOBP) and slugging (xSLG) percentages, expected ERA, barrel rate, walk rate, fastball velocity, and extension.

When the Yankees came to Fenway that October for the last single-game Wild Card round in MLB history, Cora sent his rookie reliever out to the mound for a karmic ninth inning performance; ten months after the Yankees declined to protect him from the Rule 5 draft, Whitlock ended their season.

The Red Sox ran into difficulties when they began trying to transition Whitlock to the rotation the following season. He made 19 starts and 34 relief appearances between ’22 and ’23 and missed time due to various injuries and surgeries. After earning a spot in the rotation last spring training, Whitlock looked strong in his first four starts, then needed season-ending surgery for what his doctor described as a “fluke” elbow injury.

The affable, upbeat right-hander is hoping working out of the ‘pen will help make 2025 his “Year of Health.”

“This is what I want to be the year of health for me,” he said. “Just the full 162 (games) and focus on that, and focus on staying healthy.”

“With Whit’s injury history, keeping every one of our pitchers healthy is important,” said Red Sox pitching coach Andrew Bailey. “I know he just wants to win and do anything. Getting him back on the field and being part of the team is of the utmost importance to us and his career and our team winning, and his being on the field consistently throughout the season is going to be really valuable to us.”

While the abundance of starting pitching options on the 40-man roster also factored into the decision, the Red Sox bullpen needs fortification and Whitlock has a proven track record. Boston had a meager 56% save percentage in 2024, only converting 40 of 71 opportunities. Only the Chicago White Sox, who set a new modern MLB record with 121 losses, blew more saves.

“It’s huge,” Bailey said of having Whitlock in the pen. “He’s a guy that you can hand the ball off to and have him go a couple of innings late in the game and give the back-end guys a rest. He’s a multi-inning force back there. Gives us another way to finish games.

“Not only your typical multi-inning guy cleaning up some down games or some big games, he’s a guy that can throw multiple innings in close games as well which gives AC a different way to finish ballgames, which is really valuable for us.”