Then he threw all that out the window.
The Tigers' No. 15 prospect shattered a career high with 13 strikeouts, allowing four hits over six scoreless innings as Class A West Michigan rolled past visiting Dayton, 7-1.
Carreno (9-8) had fanned eight once before this season and seven twice before mowing down the Dragons at Fifth Third Ballpark. He got stronger as the game wore on, striking out the side in the fourth and the sixth.
"He has a feel for all his pitches, has a lot of confidence out there," Whitecaps pitching coach Mark Johnson said. "He's got a good fastball, he attacked with that. He finished with his curveball, was able to throw it behind in the count, and really had a good combination of all his pitches, the changeup, too.
"[He was] reading swings, pitching to both sides of the plate. He made pitches and got swings."
The 21-year-old right-hander lowered his ERA to 3.23 in 139 1/3 innings this season, good for ninth in the Midwest League. He ranks sixth with 119 strikeouts against only 28 walks -- none on Saturday.
Carreno's also been remarkably consistent, with his ERA ranging between 2.81 and 3.75 each month.
It's been a season with a great deal of progress for the Venezuela native, according to Johnson. Last year with the Whitecaps, he went 7-10 with a 4.55 ERA 24 games, including 23 starts. In 2010 at short-season Connecticut, he posted a 4.76 ERA in 14 starts.
"He's really seemed to start to mature as a pitcher, learning to use all his stuff instead of sitting there trying to throw hard," Johnson said. "That's where you see development, maturing overall. He's made great strides forward."
The 2007 international signee spent 2008-09 in the Venezuelan Summer League, where he posted 2.82 and 2.36 ERAs, respectively. The success he showed as a teenager has finally translated to a full-season league.
Johnson said he would not be shocked if Carreno builds off his breakout season.
"I think you start him in [Class A Advanced Lakeland] and you never know from there," he said. "If he takes off, he could find himself in Double-A [quickly]. He's got good stuff, a young power arm and a very high ceiling. You don't want to rush developmental time, but he's going to get a shot up there and go from there."
Third baseman Jason King led the Whitecaps' offense with two hits and two RBIs.