GREENSBORO, N.C.—Entering this season, it would have been easy to overlook Will Stewart. After being drafted in 2015, the lefthander posted ERAs above 4.00 in each of his first three seasons—two in the Rookie-level Gulf Coast League and another with short-season Williamsport.

He wasn’t a fixture on the summer showcase circuit either, appearing in only the 2014 East Cobb Invitational before his senior season of high school in Hazel Green, Ala., a city of just more than 3,600 people.

In his fourth season, however, Stewart is beginning to show why the Phillies gave him a $100,000 signing bonus as a 20th-round selection. Over the season’s first six weeks, Stewart has gone 4-0, 1.26 with 38 strikeouts and just six walks while pitching for low Class A Lakewood.

Still, that’s not the most interesting part the 20-year-old’s season. His groundout-to-airout rate is 2.67, which is the seventh-best in the minor leagues. His groundball percentage, as measured by Fangraphs, is 64.4 percent, which is tied for the third-best in the minors.

So, what changed between last year and this year that has caused such an uptick in success? Part of it, Stewart says, has to do with his mindset on the mound.

“I’ve always had the physical talent, it’s always been there. The physical part has always been there, but my mental game has grown so enormously over this past offseason,” Stewart said after his latest start. “I come in with the attitude every time I come to the park that I’m just going to have fun, because this is a game and I don’t think we make it fun enough. I think we make it more of a job.”

That attitude was tested last Thursday night, when an error allowed Greensboro to strike first with a run that stood as the game’s only score until Lakewood rallied for four runs in the top of the ninth inning.

“Will Stewart from two years ago would have looked at everyone like, ‘Are you serious?'” Stewart said. “But I think that (new attitude) is a big deal. It’s one of the best things that I’ve changed in my repertoire so that I can handle the upsets, I can handle the bad outings and I can handle things like that. That’s a big deal to me.”

Stewart’s fastball isn’t going to jump off the page for its velocity, which topped at 92 mph on Thursday and sat more in the 90-91 range, but its late action away from righthanders has been a difference-maker. He throws both two- and four-seam fastballs, but both get two-seam bite thanks to his funky, low-slot delivery.

That low-90s velocity is also a departure from his first few years, when he sat in the high 80s. The natural, physical growth and maturity that occurs when a young man goes from 18 to 20 years old plays a part, but he has also adhered to the developmental programs set by both the Phillies and his father, who was a bodybuilder through his college years.

“I think it just came with me working out more and doing everything like that,” he said.

He couples his fastball with a changeup in which he has supreme confidence. So much so that Stewart agreed with an estimate that he didn’t throw anything other than a fastball or changeup for a stretch of roughly four innings on Thursday.

Although it’s technically classified as one pitch, Stewart really throws two versions of the same circle changeup, which he learned from his personal pitching coach Courtney Duncan, who pitched in the big leagues with the Cubs for parts of two seasons. If Stewart wants to get a grounder, he’ll throw the pitch one speed.

If he wants to get a strikeout, he’ll throw it a little harder.

“My game plan is: I’m going to go fastball-changeup until someone proves they can hit it,” Stewart said. “And until you prove it, that’s all you’re getting. I’m not going to pull out all my guns in the first inning.”

The exception to the rule on Thursday was Greensboro’s Lazaro Alonso, who received a steady diet of sliders all night. Stewart whiffed Alonso in the first inning on a slider—which is a new addition to Stewart’s arsenal—then did it again in the sixth in an at-bat that featured seven consecutive sliders.

“He was just a guy who I knew couldn’t hit (the slider),” Stewart said. “He’s a big, fastball-hitting guy. He’s big. He’s huge. He’s got the swing. He’s got the power, but it was more of a thing where I knew he couldn’t get to it, so that’s why I kept throwing them.”

If it weren’t clear by now, Stewart puts a lot of thought into how he attacks hitters. All night Thursday he used his three-pitch mix up and down, in and out to keep hitters off-balance and change their eye levels.

In the second inning against Greensboro's leadoff man, Thomas Jones, Stewart started with a fastball up and away, followed by two changeups for called strikes on the inside corner. He then finished the strikeout with another fastball up and away, which Jones swung underneath.

By varying his speed and location, Stewart got exactly what he wanted.

“That’s what we work on,” he said. “We talk about changing eye levels here because hitting’s already hard enough. If you’ve got to change eye levels, good luck.”

Throughout the entirety of the Lakewood pitching staff, which holds a 2.60 ERA, this year’s theme has involved using all of each pitcher’s weapons to exploit the opposition’s weaknesses as efficiently as possible.

“We talk a lot with our guys about identifying those things and being able to stick to them,” Lakewood pitching coach Brad Bergesen said. “I thought (Stewart) did a good job of that tonight.”