Chavez joins the Pirates after a successful season at Indianapolis, where he went 2-6 with 14 saves and a 3.80 ERA in 51 relief appearances. Those numbers improved even more so after the All-Star break, as Chavez allowed just five earned runs in 17 innings.
The 25-year-old righty came to the organization in 2006, when the Pirates traded starter Kip Wells to Texas, and despite solid results, he's gone somewhat under the radar since. Chavez's success this year mirrors his numbers from a year ago as well. He went 3-3 with a 3.92 ERA for Indianapolis in '07.
This callup marks Chavez's first taste of the big leagues.
Chavez attributed much of his improvement this season to a mechanical adjustment that he and Triple-A pitching coach Ray Searage made in Spring Training. Searage slightly adjusted Chavez's stance so that he maintained a forward momentum during his delivery to keep from flying open toward first base after releasing the ball.
"It's given me a lot more consistency down in the strike zone," Chavez said Wednesday. "Now I have a lot more consistency with my offspeed pitches."
Chavez has pitched just one-third of an inning in the past four days, giving the Pirates' bullpen a much needed fresh arm. One extra-inning affair and two uninspiring starting performances have forced the 'pen to log 16 1/3 innings in the past three days.
As for Hansen, the results simply haven't been there since he joined the club as a result of the Trade Deadline deal that sent Jason Bay to Boston. In nine relief appearances this month, Hansen allowed nine earned runs on eight hits and 12 walks. He struck out just three.
It all came to an ugly head on Tuesday night against the Cubs, when Hansen walked three, including two with the bases loaded, and gave up four runs without recording an out in the eighth.
Hansen will most likely return to the Pirates after rosters expand on Sept. 1.
To make room for Chavez on the team's 40-man roster, the Pirates transferred lefty Phil Dumatrait from the 15-day to the 60-day disabled list. Dumatrait underwent season-ending surgery on his left shoulder Aug. 8.
Jenifer Langosch is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.