"We talked about him for a number of years about having some of the best swing-and-miss stuff in the organization with an electric slider," Matheny said. "But he just had trouble repeating staying in the strike zone. He had good life typically, but also could get very erratic. It was a tough mix for him to get past."
Sanchez, 24, had one save and a 3.72 ERA in nine relief appearances for Triple-A Memphis, giving up four earned runs over 9 2/3 innings. He has spent part of the last two seasons in the big leagues with the Cards, combining to go 3-2 with five saves and a 3.40 ERA in 43 relief appearances. Sanchez has 48 strikeouts over 45 innings, and he held opponents to a .166 batting average against.
The right-hander made his Major League debut in 2011 and went 3-1 with five saves and a 1.80 ERA in 26 relief appearances.
"It's a way to get another power arm, which we don't have in the Minor Leagues," Cubs manager Dale Sveum said. "His only problem is walking guys right now. We're trying to get some power arms in this organization, and that was a really nice waiver claim -- to get a 24-year-old kid who throws 94-to-98 miles an hour with a power slider."
The move was necessary for the Cardinals, who wanted to open a roster spot for pitcher Tyler Lyons.
Carrie Muskat is a reporter for MLB.com. She writes a blog, Muskat Ramblings, and you can follow her on Twitter @CarrieMuskat. This story was not subject to the approval of Major League Baseball or its clubs.