Rienzo, 25, was 0-2 with 4.85 ERA in three starts with the Knights this season. He has allowed 15 hits, walked eight and struck out nine, after going 2-3 with a 4.82 ERA in 10 starts for the White Sox last season.
Charlotte pitching coach Richard Dotson has worked with Rienzo on lowering his arm angle upon delivery. Although it's not much of a change, Rienzo notices the difference.
"Just a little bit," said Rienzo of the change. "I try to sink the ball more and [be] consistent with more strikes, breaking ball strikes. Keep doing it and see if the results come. I feel good. The curveball, it's strikes more, so that's important."
Scott Merkin is a reporter for MLB.com. Read his blog, Merk's Works, and follow him on Twitter @scottmerkin. This story was not subject to the approval of Major League Baseball or its clubs.