Sawamura played nine seasons for the Yomiuri Giants during 2011–2020;[4] he missed the 2017 season due to a shoulder injury.[5] In 2011, he was named the Central League Rookie of the Year.[6] In 2013, he was named MVP of the first game of the NPB All-Star Series.[7] During his first four seasons with the Giants, he was predominantly a starting pitcher; after 2014, he only appeared for the Giants as a relief pitcher.[1] As a closer during 2015 and 2016, he recorded 36 and 37 saves, respectively.[4] During his nine seasons with the Giants, he compiled a 48–50 win–loss record with 74 saves.[4]
On September 8, 2020, Sawamura was traded to the Chiba Lotte Marines.[11] With the Marines in 2020, he appeared in 22 games, pitching to an 0–2 record with one save and a 1.71 earned run average (ERA) while striking out 29 batters in 21 innings pitched.[4] After the season, Sawamura became a free agent.[12]
Boston Red Sox
On February 16, 2021, Sawamura officially signed a two-year, $3 million contract with the Boston Red Sox of Major League Baseball (MLB).[13] He made his MLB debut on April 2, pitching in relief against the Baltimore Orioles.[14] He earned his first MLB win on April 23, after pitching 1+1⁄3 innings of scoreless relief against the Seattle Mariners.[15] Sawamura was placed on the injured list on July 23 due to right triceps inflammation;[16] he returned to the Red Sox on July 30.[17] He was placed on the COVID-related list on August 31,[18][19] and returned to the team on September 13.[20] Overall during the regular season, Sawamura made 55 relief appearances for Boston, compiling a 5–1 record with 3.06 ERA while striking out 61 batters in 53 innings.[21] He made three postseason relief appearances, all in the American League Championship Series, allowing a single run in two innings pitched.[21]
Sawamura began the 2022 season as a member of the Red Sox bullpen. After posting a 3.60 ERA in 18 relief appearances, he was optioned to the Triple-AWorcester Red Sox on May 28,[22] but recalled to Boston two days later.[23] On August 29, Sawamura was designated for assignment,[24] then sent outright to Triple-A two days later.[25] On September 11, Sawamura was released by the Red Sox.[26] Overall during 49 relief appearances with the Red Sox during 2022, Sawamura compiled a 1–1 record with a 3.73 ERA while striking out 40 batters in 50+2⁄3 innings.[21]