Boston Red Sox Baseball America rated Masterson as the 64th-best overall prospect for their
2006 Major League Baseball draft projections. The
Boston Red Sox selected him in the second round. Dan Madsen signed him. Masterson began as both a starter and reliever in his minor league career for the
Lowell Spinners. In 2007, his second season, the club promoted him from the Class A
Lancaster JetHawks to the Double-A
Portland Sea Dogs. His twelve wins that season ranked second among all Red Sox minor leaguers. After joining the Sea Dogs, Masterson said, "I've had the confidence to be a great pitcher all along. I went to a smaller school and really proved that I had the ability to pitch, and whatever route I took to get me where I am I'm not worried about it." In 2006, Masterson was named to
Baseball America's
short season all-star team. Masterson converted to starting pitching in early 2007, after a stint as a relief pitcher for Short Season Lowell in 2006. The Red Sox invited Masterson to
spring training before the
2008 season. On April 24, he made his Major League debut against the
Los Angeles Angels of Anaheim in an emergency call-up start. He pitched six full
innings (IP) and allowed one run. The Red Sox immediately sent him back to Portland following the game. The next month, on May 20, he made his second appearance, pitching innings, allowing three hits and one run with three walks and five strikeouts and picking up his first win in the Majors. After five starts with the major-league club, it was announced that he would stay in the majors through
Daisuke Matsuzaka's return from the
disabled list (DL) due to
Bartolo Colón's back injury. On July 7, 2008, Masterson was sent back to the Pawtucket Red Sox, a move
manager Terry Francona stated was made to transition Masterson from a starter to a relief pitcher. Masterson was recalled on July 20 due to an injury to
David Aardsma In his first relief appearance, he was solid against the Seattle Mariners, shutting down the hitters and working scoreless innings at
Safeco Field in
Seattle. Masterson picked up the first postseason win of his career in Game 5 of the
2008 American League Championship Series (ALCS) against the
Tampa Bay Rays, pitching a scoreless ninth inning in the Red Sox' 8–7 victory. In 2009, Masterson began the season in the bullpen while also starting six games before being traded to the
Cleveland Indians.
Cleveland Indians On July 31, 2009, Masterson was traded by Boston along with minor league prospects
Nick Hagadone and
Bryan Price to the
Cleveland Indians in exchange for
Victor Martinez. Upon arriving to Cleveland, Masterson was inserted into the Indians rotation. He started 10 games, struggling to a record of 1–7 for the rest of 2009. Masterson enjoyed his first full season as a starter in
2010, but he once again failed to make an impact with the Indians and finished with a 6–13 record in 29 starts. Nevertheless, Masterson seemed to save his best stuff for when he was facing his former Red Sox teammates. He pitched the first
shutout of his professional career on June 9 of that season, a two-hit, 11–0 victory against Boston at
Progressive Field, in which he struck out six and allowed two singles and two walks. Masterson finished the
2011 season with a 12–10 record, having career bests in ERA (3.21), innings pitched (216) and home runs allowed (11). On August 4, he victimized the Red Sox for the second time, and also committed one of the rarer feats in baseball. In the bottom of the second inning, Masterson struck out
Josh Reddick swinging before a
wild pitch allowed Reddick to reach first base on the play. Then, Masterson proceeded to strike out
Jason Varitek,
Marco Scutaro and
Jacoby Ellsbury in succession to end the inning, making him one of 68 pitchers in Major League history to
strike out four batters in a single inning. Following the end of the season Masterson underwent surgery to repair a torn
labrum in his non-throwing shoulder. The surgery was required after enduring an injury in 2007 as a member of the Red Sox. On April 5,
2012, the Indians made Masterson the
Opening Day starter for the first time in his career. The game was against the
Toronto Blue Jays in what proved to be the longest Opening Day game in major league history, a 7–4 loss in 16 innings. He completed eight innings, giving up two hits and one run while striking out 10, and earned a no-decision. However, he regressed in his third season with the Indians, finishing 11–15 with a career-worst 4.93 ERA in 34 starts. The Indians hired Francona to be their
manager the following October, reuniting the pitcher with his former manager. For the
2013 season, the Indians again named Masterson the Opening Day starting pitcher. He defeated
Blue Jays' reigning NL
Cy Young Award winner
R. A. Dickey, acquired in the prior off-season from the
New York Mets. In his next start, his second win came against the reigning American League Cy Young winner,
David Price of the
Rays. According to the
Elias Sports Bureau, Masterson became just the third player in MLB history to defeat both reigning Cy Young winners in the same season – and the first to do so in his first two starts of the season. With his sixth campaign about to begin and no contract, Masterson was eligible to become a
free agent for the first time in his career. He was also
arbitration-eligible. Instead, Masterson and the Indians agreed to a one-year, $9.7 million contract in February 2014, for the
2014 season. The two parties also began talks for a contract extension beyond 2014. However, the next month, discussions were ended until after the season. Masterson had offered the club extensions for $17 million per year in separate offers of two and three years, with option years, but that was more than the Indians were willing to pay. A pitcher with similar career achievements,
Homer Bailey, had signed an extension for more years with the
Cincinnati Reds at $17.5 million per year. Tapped for his third consecutive Opening Day start, Masterson pitched seven scoreless innings but did not qualify for a decision in a 2–0
extra innings victory against the
Oakland Athletics. On June 2, he completed an
immaculate inning against the
Red Sox, striking out
Jonny Gomes,
Grady Sizemore, and
Stephen Drew in order on nine pitches. Only 72 pitchers have accomplished that feat in Major League history.
St. Louis Cardinals On July 30,
2014, the Indians traded Masterson to the
St. Louis Cardinals for
outfielder James Ramsey. To honor their former teammate, all Indians players donned Masterson's high-sock style for the next game after his trade against the
Mariners. Masterson had been on the DL due to a
knee injury for nearly a month when he was traded. The Cardinals activated him from the DL on August 1. He won his Cardinals debut against the
Milwaukee Brewers the next day, a 9–7 victory, in spite of allowing five runs, seven hits and three walks in six IP. While batting, he collected his first hit and run scored of the season.
Return to Boston Red Sox A free agent after the 2014 season, Masterson agreed to a one-year deal with Boston worth $9.5 million on December 11. On August 10, 2015, Masterson was
designated for assignment by Boston. The first move of new general manager
Dave Dombrowski was his release on August 19.
Pittsburgh Pirates On April 14, 2016, Masterson agreed to a minor league deal with the
Pittsburgh Pirates organization. He played in 25 games for the Triple–A
Indianapolis Indians, recording a 4.97 ERA with 32 strikeouts in innings pitched. He elected free agency following the season on November 7.
Los Angeles Dodgers On March 27, 2017, Masterson signed a minor league contract with the
Los Angeles Dodgers and he was assigned to the Triple-A
Oklahoma City Dodgers to begin the season. He pitched in Triple–A all year and was 11–6 with a 4.13 ERA in 25 starts. He elected free agency following the season on November 6. On December 11, 2018, Masterson announced his retirement from professional baseball. ==Pitching profile==