Clase signed with the San Diego Padres as an international free agent on February 11, 2015, for a $125,000 signing bonus.[2] He played for the DSL Padres in 2015, going 2–1 with a 1.99 ERA in 54 innings. In 2016 he played for the AZL Padres, going 2–0 with a 4.01 ERA in 24+2⁄3 innings. In 2017 he played for the AZL Padres (2), going 2–4 with a 5.30 ERA in 35+2⁄3 innings, and in one game with the Tri-City Dust Devils of the Low–ANorthwest League, allowing 5 runs in 3+1⁄3 innings.[2]
On August 2, 2019, the Rangers selected Clase's contract and promoted him to MLB.[6][7] He made his MLB debut on August 4, pitching 1+2⁄3 scoreless innings.[8] Clase produced a 2–3 record with a 2.31 ERA and 21 strikeouts over 23+1⁄3 innings in 2019.[9] His cutter was on average the fastest in MLB, at 99.2 miles per hour (159.6 km/h).[10]
On December 15, 2019, the Rangers traded Clase and Delino DeShields Jr. to the Cleveland Indians in exchange for Corey Kluber and cash considerations.[11] Kluber pitched one inning for the Rangers before injuring himself and later departing when the 2020 season ended. Clase was suspended for 80 games on May 1, 2020, after testing positive for Boldenone, a banned PED.[12] Due to the COVID-19 pandemic and the shortening of the 2020 Major League Baseball season to 60 games, Clase's suspension was lifted at the conclusion of the shortened 2020 season.[citation needed]
Clase returned to the Indians' bullpen for the 2021 season. After converting all six save opportunities in August and holding opposing batters to an .095 average, he was named AL Reliever of the Month.[13]
On April 2, 2022, Clase agreed to a five-year $20 million extension with the Cleveland Guardians.[14] In July 2022, Clase was named to his first career All-Star team. He pitched the ninth inning for the American League at Dodger Stadium and struck out the side to get the save and secure a 3–2 victory.[15] In 2022 he was 3–4 with a 1.36 ERA in 72.2 innings, and led MLB in saves. He compiled 42 in 46 opportunities.[16]
Clase was selected to his second All-Star team in 2023.[citation needed]
