Elías pitched two seasons for Guantánamo in the Cuban National Series. In the 2008–09 season, he pitched 31 innings in 18 games, compiling a 2–3 record with a 7.84 earned run average. In the 2009–10 season, he had a 7.14 ERA with 5–7 record while pitching 63 innings in 21 games. Elías defected from Cuba in 2010, hoping to sign a contract with a Major League Baseball team. He traveled 30 hours by boat from Cuba to Cancun, Mexico. He initially played on the "B" team of the Sultanes de Monterrey in the Mexican League.
Seattle Mariners
Elías signed a minor league contract with the Seattle Mariners on May 3, 2011. He made his minor league debut that season and pitched for the Rookie LeaguePulaski Mariners and Arizona League Mariners, and the Single-AClinton LumberKings. Overall, he went 5–2 with a 4.28 ERA and 41 strikeouts over innings pitched. In 2012, he played for the Class A-AdvancedHigh Desert Mavericks. He started 26 games, finishing with an 11–6 record, 3.76 ERA, 128 strikeouts over innings pitched. He played the 2013 season with the Double-AJackson Generals. He started 22 games, had a 6–11 record and 121 strikeouts over 130 innings. Invited to spring training by the Mariners in 2014, Elías competed for a rotation spot on the Mariners' Opening Day roster, making the team as one of the starting pitchers. Elías made his Major League debut April 3, 2014. Against the Detroit Tigers on June 1, Elias recorded the team's first shutout by a rookie since Freddy García in 1999. For the 2014 season, Elías pitched in 29 games for the Mariners, compiling a 10–12 record with 3.85 ERA in innings pitched. During the 2015 season, Elías made 22 appearances for Seattle, pitching innings with 4.14 ERA while compiling a record of 5–8. He also made 12 starts for the Triple-ATacoma Rainiers, with a 4–2 record and 7.34 ERA in innings pitched. Overall for the Mariners, Elías appeared in 51 MLB games with a 15–20 record with 3.97 ERA in 279 innings pitched.
On December 7, 2015, the Mariners traded Elías and Carson Smith to the Boston Red Sox for Wade Miley and Jonathan Aro. Elías made his Boston debut in relief on April 23, 2016, against the Houston Astros. In June, he was called up from the Triple-A Pawtucket Red Sox and faced his former teammates in his first starting appearance with the Red Sox on June 17, giving up seven runs over four innings. Elías was optioned back to Pawtucket after the game. He made one additional appearance for Boston during the season, pitching two innings of one-run relief against the Arizona Diamondbacks on August 16. Overall, for the 2016 season, Elías made three appearances for Boston, pitching innings with a 12.91 ERA and 0–1 record. Elías started the 2017 season on the disabled list, due to a muscle strain suffered in early March. After missing several months of the season, he played with four different Red Sox farm teams; the Single-A Lowell Spinners and Salem Red Sox, Double-A Portland Sea Dogs, and Triple-A Pawtucket. For those four teams, he pitched a total of innings in 10 games with a 6.96 ERA and a 1–6 record. Late in the season, he made a single appearance for Boston, pitching of an inning on September 4 against the Toronto Blue Jays; he walked one batter and struck out one batter. Elías started the 2018 season with Triple-A Pawtucket, where he appeared in four games in relief, pitching a total of innings with a 1.23 ERA, 1–0 record, and one save. Overall for the Red Sox, Elías appeared in 4 MLB games with a 0–1 record with 12.38 ERA in 8 innings pitched.
Second stint with Mariners
On April 23, 2018, the Red Sox traded Elías to the Seattle Mariners for cash. After reporting to Triple-A Tacoma, he went 2–4 with a 4.94 ERA with 27 strikeouts and 12 walks in 7 games. On June 1, 2018, Elías was called up from Tacoma to make his season debut against the Tampa Bay Rays, in which he tossed two scoreless innings in relief, earning the win. Throughout the season, Elías was typically used as a long reliever or spot starter, finishing 2018 with a 2.65 ERA, 154 ERA+, 3.08 FIP, and 2.13 strikeout-to-walk ratio in 23 appearances, including 4 starts. Following the departure of All-Star closer Edwin Díaz in the 2018 offseason as well as an early-season injury to newly-acquired closer Hunter Strickland, Elías was used exclusively out of the bullpen especially in high leverage situations, ultimately becoming the team's new closer. In 44 games with the Mariners in 2019, he pitched to a 3.64 ERA with 14 saves. 45 strikeouts, and 17 walks.
Washington Nationals
On July 31, 2019, the Mariners traded Elías and Hunter Strickland to the Washington Nationals in exchange for Aaron Fletcher, Taylor Guilbeau, and Elvis Alvarado. Elías made his Nationals debut on August 2, 2019, recording the final two outs of the sixth inning. However, he was forced to leave the game and was placed on the 10-day injured list after he pulled his right hamstring running down the first-base line during an at-bat the following inning. In 2019 he pitched three innings for the Nationals. Between the Mariners and the Nationals combined in 2019, he was 4-2 with 14 saves and a 3.96 ERA, as in 48 relief appearances he pitched 50.0 innings. The Nationals finished the 2019 year with a 93-69 record, clinching the wild card, and eventually won the World Series over the Astros. Elias was not part of the Nationals' postseason run, but still won his first world championship.
