The back end of the bullpen continued to generate a high return for the rebuilding Brewers, as the club traded reliever Tyler Thornburg to the Red Sox for Travis Shaw and two prospects on Tuesday.

In exchange for Thornburg, Milwaukee acquired Shaw, a 26-year-old who will probably become the starting third baseman, as well as pitcher Josh Pennington, shortstop Mauricio Dubon and either a player to be named or cash from Boston. The announcement was made from baseball's Winter Meetings in Maryland by general manager David Stearns.

Thornburg pitched well after becoming the closer following the Aug. 1 trades of late-inning arms Jeremy Jeffress (along with Jonathan Lucroy) to Texas and Will Smith to San Francisco. The former starter, who was among the club’s top prospects at one time, made a career-high 67 appearances last season, going 8-5 with 13 saves and a personal-best 2.15 ERA. He was arbitration-eligible for the first time, and no doubt was due for a raise from his 2016 salary of $513,900.

As was the case in Stearns’ trades of Jeffress and Lucroy to the Rangers and Smith to the Giants – along with several other veterans-for-prospects deals the young GM has executed over the past 13 months – the yield for Thornburg was impressive, at least on paper.

In 145 games last year, his first full Major League season, Shaw had a slash line of .242/.306/.421, despite a late swoon. Making 99 starts at third base and 28 at first, the left-handed batter finished with 16 home runs, 34 doubles and 71 RBI. He had five RBI in a game four times in 2016, which was tied for the most such games in the majors. Shaw had an OPS of only .599 against left-handed pitchers, making a righty-lefty platoon with Hernan Perez a likely scenario.

Last year, Milwaukee primarily used Perez and stolen-base leader Jonathan Villar at third. The Shaw move could mean Villar slides over to second base – the Brewers last week signed Scooter Gennett to a $2.5 million contract for 2017 in his first season of arbitration eligibility but could look to trade the 26-year-old – and the versatile Perez perhaps becomes an offensively inclined utility man.

Besides Shaw, the Brewers also received Dubon and Pennington. Stearns has said often that his goal is to acquire young, controllable talent to develop in Milwaukee’s now top-ranked farm system for the club’s return to contention in the future. Dubon is a 22-year-old shortstop who was ranked No. 12 in MLBPipeline.com’s list of Boston’s prospects, and Pennington, a 21-year-old right-hander, was ranked No. 22.

"We are pleased to add three young and talented players to the organization," said Stearns. "Travis provides another left-handed power bat, bringing balance to the lineup. Mauricio is a highly-regarded prospect who brings us speed and plate discipline, and adds further infield depth. Josh is a promising young prospect who further improves our stock of power arms throughout the system."

Dubon hit .323 with six home runs, 69 RBI and 30 stolen bases in 124 games last year, playing 62 each at Class-A Salem and Double-A Portland. In 330 games over four minor-league seasons, he batted .306 with 14 home runs, 154 RBI and 73 stolen bases. A Carolina League All-Star at Salem who recently played in the Arizona Fall League, Dubon was ranked by Baseball America as the seventh-best prospect in the Red Sox organization after the 2016 campaign.

Though the Brewers last season called up prized shortstop Orlando Arcia, who should have the job for years to come, Stearns has been fond of acquiring young players at the position because their athleticism allows them to be recast elsewhere. Dubon, for instance, could have a future in centerfield.

Pennington went 5-3 with a 2.86 ERA in 13 starts at Class-A Lowell in 2016, after going 2-1 with a 0.82 ERA in six starts with the Gulf Coast League Red Sox in 2015. Over two minor-league seasons, he has held opponents to a .205 batting average with 71 strikeouts in 78.2 innings pitched.

Last year, the Brewers sent Jeffress and Lucroy to Texas in exchange for two highly regarded minor-league prospects, outfielder Lewis Brinson and pitcher Luis Ortiz, and dealt Smith to San Francisco for catcher Andrew Susac and picher Phil Bickford, who was the Giants' 2015 first-round draft pick.

Stearns and manager Craig Counsell said after last season that they wanted to attain better lineup balance, and after signing Eric Thames last week and acquiring Shaw, they now have lefties at both corner infield spots. So for the short term, Milwaukee gets another big lefty bat, and one the team controls for two more years before he’s eligible for arbitration, without having to pay for Thornburg, a veteran reliever they don’t really need if they aren’t planning to compete for the playoffs in 2017.

But it’s all about the long-term future for Stearns and the Brewers, and getting Dubon and Pennington – plus the cash or player to be named – adds more potential-filled pieces to the puzzle they hope to eventually have rebuilt.