MIAMI -- The Cardinals' exploration for bullpen help took them in the same direction it has in recent years, with general manager John Mozeliak passing on the top-tier of available arms to find an upgrade that didn't come with as high an acquisition cost.
This year, that addition is lefty Zach Duke, whom the Cardinals acquired from the White Sox on Sunday, a little more than 24 hours ahead of the non-waiver Trade Deadline. The Cardinals flipped Minor League outfielder Charlie Tilson to Chicago to complete the swap.
"When you look at where our needs are, he will fit in ideally," Mozeliak said of Duke, who will join the club on Tuesday. "I think when you look at the reliever market, there is the [Aroldis] Chapman - [Andrew] Miller group. We felt the Zach Duke's of the world were right below that. There weren't many of them available, and we felt like this was a good get for us."
Miller came off the board of available relievers just before the Cardinals finalized their deal with Duke. And like Chapman a week ago, it took a package of four prospects to pry him away from the Yankees.
The Cardinals lost only Tilson, a 23-year-old outfielder who had been added to the organization's 40-man roster last November but who had not yet ascended to the Majors. Tilson hit .282 with four homers and 34 RBIs in 100 Triple-A games this season but had faded from the organizational outfield depth chart with the surprise emergence of Jeremy Hazelbaker and the quick climb of Harrison Bader.
The acquisition cost was more palatable for Mozeliak, too, because Duke is under contract for another season. He is due $5.5 million in 2017 after making $5 million this year.
"[I] was not looking for a rental," Mozeliak said. "We wanted someone who would give us some depth not only for today but for tomorrow."
Duke, 33, has made an American League-leading 53 appearances this season and posted a 2.63 ERA and 1.25 WHIP over 37 2/3 innings. The White Sox have used Duke largely in a setup role -- not as a lefty specialist -- and that mirrors the Cardinals' plans for him.
Mozeliak and manager Mike Matheny said they envision fitting Duke into the setup mix along with Kevin Siegrist and Jonathan Broxton. Having another back-end-of-the-bullpen arm can help the Cardinals avoid overusing their three most reliable late-game relievers.
"I played against the Cardinals for a long time and was always envious of how well they played the game of baseball," Duke said. "They did everything right. They hardly ever made mistakes. So now I'm going to get to experience their process and the way they do things and kind of what makes them so successful year in and year out. It's exciting."
Duke has limited right-handed batters to a .182 average and .658 OPS this season, while lefties have hit .264 and posted a .646 OPS against him. Since the start of July, Duke has allowed two earned runs in 13 appearances.
Duke reinvented himself into an effective reliever after a mediocre career as a starting pitcher with the Pirates. From 2005-10, he went 45-70 with a 4.54 ERA in 160 games (159 starts) for Pittsburgh. Pitching exclusively in relief over the last three seasons, Duke has compiled a 2.87 ERA.
"From a scouting standpoint, we just had a lot of positive reports on him," Mozeliak said. "He was someone we identified early on. We just didn't necessarily think we would be able to get something done given where the market was headed. I think we could have ended up adding someone else to the bullpen, but it just wouldn't have had the kind of impact of those late innings."
The Cardinals will add Duke to the roster on Tuesday and make a corresponding move at that time. Those will be among several moves the club plans to make ahead of its series opener in Cincinnati. Brandon Moss (left ankle sprain) and Jhonny Peralta (left thumb ligament strain) are also expected back on that date.
As for whether the Cardinals will engage in any other trade activity ahead of Monday's non-waiver Deadline, Mozeliak cast that as doubtful.
"Done is always a bad word to use in this business," Mozeliak said. "I feel like we've addressed our biggest need, but as we look at the next 30 hours, we remain open-minded, and we'll see. But I'm not aggressively pursuing anything at this point."
Jenifer Langosch has covered the Cardinals for MLB.com since 2012, and previously covered the Pirates from 2007-11. Read her blog, follow her on Twitter, like her Facebook page and listen to her podcast. This story was not subject to the approval of Major League Baseball or its clubs.