BOSTON — The Cleveland Guardians are headed to the postseason for a third straight year after a 1-0 victory over the Boston Red Sox on Thursday night, sealed by Angel Martínez’s second-inning home run. Martínez’s 18th homer of the season was all Cleveland needed. Joey Cantillo, working in a bulk relief role, followed starter Daniel Espino and held Boston to one hit over five innings, striking out four. Cantillo has now thrown 15 consecutive scoreless innings since leaving the rotation. Cade Smith finished the shutout by striking out all three batters in the ninth. His save was his major-league-leading 41st of the season. The win guarantees Cleveland at least an American League wild-card spot. The Guardians also hold a one-game lead over the Chicago White Sox in the AL Central, with the division title still in play. Chicago owns the head-to-head tiebreaker, making the remaining games significant: the division winner is likely to receive the league’s No. 2 seed and a first-round bye into the Division Series. Boston, which had already clinched a playoff berth for a second consecutive season, managed just two hits and was shut out for the eighth time this year. Red Sox starter Ranger Suárez allowed one run in five innings and struck out five. Boston leads Chicago by three games for the AL’s second wild-card position, which would place it in a best-of-three series against the No. 4-seeded New York team. Cleveland is scheduled to open a three-game series in Kansas City on Friday, with Gavin Williams listed as the probable starter. Boston is set to host the Chicago Cubs for a Friday doubleheader; starters had not been announced.