DETROIT – Kohl Stewart did not rocket through the Twins farm system. He had to develop other pitches. He had to alter his conditioning. He had to change his mental approach.

He had to grind.

"I think if it had come easy it wouldn't have been as satisfying," Stewart said, "and I've had plenty bumps in the road and there's a lot of things I need to do better at."

Stewart, 23, is not the kid with the blazing fastball the Twins hoped they were drafting when they made him the fourth overall pick in 2013. Instead, he's a ground-ball-inducing, home-run-avoiding righthander who is learning how to pitch. And he finally will get his taste of the majors on Sunday when he faces the Tigers.

It's the culmination of five-plus years of making incremental improvements while working his way to the majors.

He went 3-7 with a 4.47 ERA between Class AAA Rochester and Class AA Chattanooga this season. He posted a 1.48 ERA over four outings at Chattanooga to get promoted to Rochester. In July, he had a 1.46 ERA over four outings that got the Twins' attention.

"His was one of the names these guys tabled because of how he's been pitching, particularly as of late," Twins manager Paul Molitor said. "He's kind of learning how to use his stuff and some of the things he's trying to make adjustments with, including his fastball."

Before the season, the Twins met with Stewart about those adjustments. He looked at data that revealed that he throws too many fastballs. And they wanted him to throw a one-seamed sinking fastball, which often provides more downward movement, than the two-seamer he was using.

Stewart was all ears.

"I'm not as smart as some of the people they have looking at those things," he said. "When they do come to me with something and ask me to make some adjustments, I'm going to trust what they have to say."

Stewart always has kept the ball on the ground, allowing just 24 home runs in 570⅔ minor league innings. But his ground ball rate was more than 57 percent at both minor league stops this season, a figure that would lead the majors.

"He started throwing that one-seamer," Chattanooga manager Tommy Watkins said, "and I think he liked it."

Stewart had a shoulder impingement in 2014, a sore elbow in 2015 and pitched last season with a sore knee that, now he says, was unwise. He's since taken his health more seriously.

"Some of those things you can't control and sometimes you need to look at the ways you are training," he said, "and I had to make some changes and give myself an opportunity to stay healthier for a full season."

It took a while for the changes to take hold, but his health and pitching have improved. He's more comfortable with the one-seam fastball, but he also throws a curveball, slider and changeup.

Scouts rated his slider as his second-best pitch coming out of St. Pius X High School in Houston. Stewart said on Saturday that it's his fourth-best pitch now, behind his fastball, curve and change.

Change wasn't easy, and he didn't do it alone. He also credited his wife, Genny, for helping him remain levelheaded when he wasn't performing well.

"Sometimes you can come home to a wife who tells you to get over yourself every now and then, it is probably a good thing," Stewart said. "She's the X-factor."

All of it was worth it earlier this week when he was about to dine with his parents, who were visiting him in Rochester. That's when he spoke by phone with Red Wings manager Joel Skinner and learned he was being called up.

Now about 30-40 friends and family members will be on hand Sunday for his major league debut.

"I feel like I'm ready now more than I ever have been," Stewart said. "I'm just really excited and grateful that they gave me the opportunity to come up here and start."