"I think it's more just a confidence thing," Mathes says when asked to explain his improvement since then. "Last year, I didn't really know what to expect. I was kind of tentative to pitch selection and what I was (throwing). Now I just go out and challenge guys; I'm not afraid of contact. I think last year I was more afraid of giving up runs.
"This year … ‘here it is, let's see what you can do with it,'" he said.
Iowa pitching coach Mike Mason has another explanation for Mathes' success.
"I think last year he got by with fastballs and changeups, and this year he's kind of expanded to cutters and curveballs," said Mason. "He's added a slower curveball this year that's kind of given him a slower pitch so that they've got to jump out on him.
"Generally … what's happening is J.R. is not showing them the first two times (through the order) how he is going to try to get them out the third time. I think last year, fastball and changeup, after seeing it three times they pretty much know that they're going to shoot it to right. Now, he's added a cutter that he's starting to beat guys inside with and that opens up the outside corner when he needs it."
But whether it's all a matter of confidence, adding new pitches or a combination of both, things have been on the up and up for Mathes in his second season at Triple-A. He hasn't lost in almost three months; not since May 4. Since then, he is 6-0.
Moreover, Mathes is unbeaten at home this season (4-0 with an ERA just under three points), and Mason attributed that to Mathes' ability to induce groundball outs.
Keeping his walk totals down is another important part of Mathes' game, and he's done that by issuing only 24 free passes through 99 1/3 innings overall.
Mathes has never been an overpowering pitcher, and he seems fine with that.
"I make the guys put the ball in play," the southpaw said. "I feel like my command of the strike zone is a lot better (in 2008) because last year I was not able to hit my spots. … This year, I know if its 3-0 and I'm behind in the count, I can still paint the fastball down and away or wherever I need really."
While Mathes has made the bulk of his appearances in the Iowa rotation, he's also helped the team -- and perhaps himself -- in relief this season by appearing in five games from the bullpen.
"They (Cubs) told me, ‘You've got a few other guys ahead of you as a starter, and as a left-handed guy out of the bullpen there obviously aren't very many people ahead of you,'" recalled Mathes. "We gave it a shot and I definitely didn't mind it. I took it in stride and thought I did well."
From here through the rest of the season, Mathes says he has only marginal goals. He also said that thinking ahead to Chicago is not an option right now; perhaps because moving up to the big league club this season is not a realistic scenario.
"I really never even think about Chicago," he said. "They're doing well right now and guys that haven't had any big league experience, it's going to be tough to even get there because they want to win and want guys that have been there.
"Right now, it's one of those things where I have to prove myself and do battle and then force them to have to make a decision."
InsideTheIvy.com staff writer Luke Plansky in Des Moines contributed to this report.