In 2023, Guerrero was assigned to the Double–A Portland Sea Dogs to begin the year.[3] On June 30, 2023, Guerrero was selected to play in the All-Star Futures Game, replacing teammate Shane Drohan, who was sidelined with a calf ailment.[4] In September, Guerrero was recognized as the Red Sox' minor-league reliever of the year for 2023.[5] On the season, he posted a 1.81 ERA with 59 strikeouts and 18 saves in 43 relief appearances for Double–A Portland prior to his promotion. In 6 appearances for the Triple–A Worcester Red Sox, he posted a 7.71 ERA with 9 strikeouts and one save in 4+2⁄3 innings of work.[6]
Guerrero began the 2024 campaign with Worcester, compiling a 5–3 record and 3.31 ERA with 79 strikeouts over 54+1⁄3 innings pitched. On September 6, 2024, Guerrero was selected to the 40-man roster and promoted to the major leagues for the first time.[7]
Personal life
Around age 1, Guerrero underwent knee surgery and spent around 9 months in the hospital. Since then, he has had limited knee mobility because his muscles in that area did not grow like the others.[8]