"I didn't trust my curveball to save my life," he said.
That's not the case this year, as Shields has used the extra offspeed pitch to help him collect seven complete games on his way to becoming an All-Star for the first time in his career. Now, he is trying to help his teammate Jeremy Hellickson do the same thing.
Before Hellickson's last start, Shields worked with the rookie on his curveball, changing his grip. The results were evident as Hellickson turned in seven innings and allowed just two runs, while striking out seven Yankees on Tuesday.
Two of those punchouts came on Hellickson's revamped curveball.
"What I thought I saw [Tuesday] was better depth on the hook," manager Joe Maddon said.
Hellickson changed his grip so that he uses his middle finger to spin the baseball more than he used to on his curve.
"We changed his grip up a little bit," Shields said. "He has got a really good curveball. I just think that he wasn't trusting it as much as he wanted to. He put the time and the work in to be able to do what he did."
Despite all of that, Hellickson still doesn't feel comfortable enough with the pitch to throw it early in the count.
"I feel like it's a good pitch for me right now with two strikes," he said. "I'm still working on throwing it for [early] strikes."
With an above-average fastball and changeup as part of his repertoire, the development of Hellickson's curveball is vital to the 24-year-old's future in the Majors.
"Being able to use that curveball, it allows him to throw three quality pitches," Shields said, "and they're all plus pitches."