Mella signed with the San Francisco Giants organization as an international free agent on May 31, 2012.[1] He made his professional debut in 2012 with the Dominican Summer League Giants, recording a 3–3 record and 2.47 ERA in 14 appearances. Mella played the 2013 season with the AZL Giants, logging a 3–2 record and 2.25 ERA in 10 games. He split the 2014 season between the Single-A Augusta GreenJackets and the Low-A Salem-Keizer Volcanoes, pitching to a cumulative 4–4 record and 3.45 ERA with 83 strikeouts in 86.0 innings of work.[2][3] He was assigned to the High-A San Jose Giants to begin the 2015 season.
Cincinnati Reds
On July 30, 2015, the Giants traded Mella and Adam Duvall to the Cincinnati Reds in exchange for Mike Leake.[4] He finished the year with the High-A Daytona Tortugas, logging a 3–1 record and 2.95 ERA in 4 games with the team. In 2016, Mella split the year between Daytona and the Triple-A Louisville Bats, posting a 9–9 record and 3.76 ERA with 101 strikeouts in 138+2⁄3 innings pitched.[5]
On November 19, 2016, the Reds added Mella to their 40-man roster to protect him from the Rule 5 draft.[6] He split the majority of the 2017 season between the Double-A Pensacola Blue Wahoos and Louisville, accumulating a 9–4 record and 3.00 ERA in 21 games. On September 12, 2017, Mella was promoted to the major leagues for the first time. He made his MLB debut on September 20, pitching 2 innings of 2-run ball against the St. Louis Cardinals. He finished his rookie season with a 6.75 ERA across 2 appearances for Cincinnati. In 2018, Mella spent the majority of the year in the minors, and pitched in four big league games for the Reds, stumbling to an 8.68 ERA in four games. Mella played in Louisville for the majority of the 2019 season, and allowed three runs in 3+2⁄3 innings of work in two major league games. On November 4, 2019, Mella was outrighted off of the 40-man roster[7] and elected free agency.[8]
Arizona Diamondbacks
On November 8, 2019, Mella signed a minor league contract with the Arizona Diamondbacks organization, and was invited to major league Spring Training. On September 1, 2020, the Diamondbacks selected Mella's contract to the active roster.[9] In 11 games for the Diamondbacks in 2020, Mella pitched to a 1.80 ERA with 10 strikeouts over 10 innings pitched.[10] On February 26, 2021, Mella was designated for assignment after the signing of Tyler Clippard was made official.[11] On March 1, Mella was outrighted and invited to Spring Training as a non-roster invitee.[12] After recording a 3.86 ERA in 11 games for the Triple-A Reno Aces to begin the year, Mella was selected to the active roster on June 15.[13] In 2 games for Arizona, Mella struggled tremendously, allowing 6 earned runs in 1.2 innings to the tune of a 32.40 ERA. He was designated for assignment on June 18.[14] On July 28, Mella was released by the Diamondbacks.[15]
Pittsburgh Pirates
On August 3, Mella signed a minor league contract with the Pittsburgh Pirates. He was assigned to the Triple-A Indianapolis Indians.[16] Mella made 16 appearances for the Triple-A Indianapolis Indians, going 2–0 with a 7.11 ERA and 23 strikeouts. On October 13, Mella elected free agency.[17]
On March 4, 2023, Mella signed with the Sultanes de Monterrey of the Mexican League.[20] In 28 games 28.2 innings of relief he went 1-1 with a 2.51 ERA with 16 strikeouts and 6 saves.
In 2024, Mella returned for a second season with Monterrey. He was released on October 1, 2024.[21] In 33 games 29.2 innings of relief he went 3-1 with a 4.55 ERA with more walks (17) than strikeouts (7).