"We had him do a lot of video analysis and bullpen work with his (Double-A) pitching coach and our minor league pitching coordinator," Bush said. "Jeff quickly recognized (his mistakes) and made the necessary adjustments, and regained the form that he showed in spring training and in the first month of the season."
That coincided with a late-June promotion to Iowa, where Samardzija was 4-1 with a 3.13 ERA and 40 strikeouts to 16 walks in 37 1/3 innings.
In six outings with Iowa, Samardzija turned in five quality starts. That was quite an upgrade from his struggles in Double-A, when he walked 26 hitters over the course of six starts from late April to late May and was sent to the bullpen briefly.
He finished with a 4.86 ERA, 71 hits and 42 walks in 76 innings at Tennessee.
"He's got very good movement; is repeating his delivery better; is not as visible to hitters as he was earlier, and that's why he had the inordinate amount of hits (at Tennessee). He's not as visible anymore," said Cubs Scouting Director Tim Wilken.
Also of note according to Wilken, who saw Samardzija pitch in a game against Albuquerque on June 29, is Samardzija's progression with his slider and splitter.
"There's a little more depth to it (the slider)," Wilken said. "He's shown an average changeup and has a good feel for it, and he's tinkering with a split and the split just disappears at times. I would say there's good light at the end of the tunnel here."
"He's getting more groundballs now because hitters can't pick the ball up as quickly. That's because he's repeating his delivery better," added Wilken.
Samardzija's most recent outing for Iowa was perhaps his best to date. He went six innings, surrendering one run and two hits, and tied a career-high nine strikeouts in a game against the Nashville Sounds this past Sunday at Principal Park.
"He's got major league stuff," Iowa pitching coach Mike Mason declared after watching that game. "What he's learning to do is get ahead and put them away with his (splitfinger). And that's been pretty much, at this level, a dominant pitch.
"He's got an out-pitch for late in the count, and he's able to throw his other stuff to get back into the count. He's developing real well as a pitcher."
At Iowa, Samardzija was consistently hitting 92-94 mph with his fastball, and he topped out at 97 mph, Cubs officials said.
The Cubs selected Samardzija, a two-sport athlete at Notre Dame, with their fifth-round draft pick in 2006 and signed him to a five-year, $10 million major league contract in January, 2007. He's come a long way since then; from averaging over one hit per inning at Class-A Daytona to his first big league promotion a year later.
"It's not surprising that he could adjust quickly because he's a tremendous athlete with great aptitude that can quickly implement mechanical adjustments," said Bush.
"Although he's very mature, he's still young in terms of actual time spent on the mound and he absorbs instruction easily. He's extremely competitive and has the make-up to be constantly challenged as he progresses through the system."
To coincide with Samardzija's call-up, Chicago placed right-hander Kerry Wood on the 15-day disabled list with a blister on his right index finger Thursday.
Samardzija will be available for Friday's game against the Marlins at 1:20 p.m. CT.
InsideTheIvy.com staff writer Luke Plansky in Des Moines contributed to this story.