Duke, a former starter who has pitched mostly in relief the last four seasons, posted a strong season out of the bullpen last season with the Milwaukee Brewers. He not only delivered a 2.45 ERA over 58 2/3 innings, but his 74 strikeouts were nearly double what he had recorded the past three seasons combined.
Duke limited opponents to a .223 batting average in 2014, including a .198 mark from the left side. He allowed just 19.5 percent of his inherited runners to score.
"In our opinion, he was one of the most desirable relievers out on the market," general manager Rick Hahn said. "It addresses a clear need for us given our performance last season. He was a player that we targeted very early in the process that we were aggressive on and needed to be given his popularity in the market."
The 31-year-old Duke has 10 years of major league experience but has never pitched for an American League team. He is still well-versed in all things White Sox, mentioning guys such as Chris Sale, Jose Quintana, Avisail Garcia and Adam Eaton, and he was interested in joining a club on the rise.
"I just feel like the athletes are there for the opportunity for this team to be successful," Duke said. "The groundwork is laid, and as Rick said, there's a few pieces missing that he's going after aggressively. I feel like the opportunity is definitely going to be there for us to make a difference in the division. As you know, the AL Central is up for grabs every year."
Duke was a starter for the first six years of his career in Pittsburgh, where he went 45-70 with a 4.54 ERA. He led the National League with 16 losses in 2009, a year when he actually made his only All-Star Game appearance. Duke has also pitched for the Arizona Diamondbacks, Washington Nationals, Cincinnati Reds and Brewers since 2011.
The White Sox struggled out of the bullpen last season, especially from the left side. Scott Downs was the primary left-handed reliever at the start of the year, but his struggles (6.08 ERA in 23 2/3 innings) led to his release in July.
Of all the left-handed relievers the White Sox used last season, Eric Surkamp had the lowest ERA at 4.81 over 24 1/3 innings.
The White Sox's 4.38 ERA from the bullpen was 14th in the AL, only better than the Houston Astros' 4.80 mark. Opponents batted .265 against White Sox relievers, second worst in the AL to the Detroit Tigers' .270 mark. No team had fewer than the White Sox's 379 strikeouts from the bullpen.
"We're real pleased with [signing Duke], but we're on to the next one now," Hahn said. "It was an important get, one we're all very happy about, but we're not deluding ourselves that we're, by any means, finished addressing our needs both in the bullpen or elsewhere. We're very happy today, but once this [conference] call is over, we'll get back on the phone."