Jordan Hicks can't explain where the gas comes from. If he's being honest, the St. Louis Cardinals rookie flamethrower doesn't really want to. Best not to overthink it.

So the 21-year-old reliever steps on the rubber and lets his mind go blank before beginning a delivery that looks like it could fit in a phone booth. No long levers. No exaggerated windup. Just straight fire stuff that makes the readout from the radar gun look like a misprint.

101. 102. 103. 104. 105.

It's the kind of speed that sends a jolt through the crowd and the opposing dugout alike. The kind that allowed Hicks to bypass Double-A and Triple-A entirely on his way to The Show.

Even the heir apparent to New York Yankees closer Aroldis Chapman as the hardest-throwing arm in the majors can't help but peek up after letting one rip.

"I like to see because I know I just put that much effort into it, what did I get out of it?" Hicks said. "What was the final outcome?"

Typically, outs. Relying on a two-seam fastball that frequently reaching triple digits, Hicks is 2-1 with a 1.75 ERA in 24 games this season for the Cardinals, one of the constants in a bullpen that's been erratic at best. The learning curve is still in progress Hicks has 16 walks against 11 strikeouts in 24 2/3 innings but Matheny is encouraged that Hicks is trying to truly pitch instead of focusing on lighting up the gun.

While Matheny understands the attention that comes with Hicks' feats like when he threw five consecutive pitches at 103 mph and above to Philadelphia's Odubel Herrera on May 20 he's just as pleased with Hicks' mentality. Three days after going heavy to Herrera, Hicks struck out two batters in an inning of work against the Kansas City Royals.

"I was afraid he was going to try and hit 112, but he came out and probably had his best outing," Matheny said. "And it was under control, but it still wasn't holding back, but it was in the zone. Those are the things that we need. He can throw as hard as he wants to but control counts and have a purpose of why you're making a pitch and not to just `wow' the watching world."

Hicks is actually doing a little of both.

Pittsburgh Pirates second baseman Josh Harrison likes to stand his ground in the batter's box, a philosophy that ended with him getting hit 23 times last year, the second-highest total in the majors. He was warned by teammate Jordy Mercer about the way Hicks' fastball runs in on right-handed hitters, but still he dug in as usual against Hicks for an at-bat Saturday.

On the first pitch, Hicks sent 101 mph whizzing inches from the pinky finger in Harrison's left hand, the one Harrison broke after getting drilled by Miami's Jose Urena. He wasn't quite so comfortable after that.

"It comes out hot, I'll tell you that," Harrison said. "The first one, you can go back and look at the replay, when I took it, I pulled my hands in and I said `Ooooooh."'

Harrison worked the count full before grounding out to second base. He walked away equal parts frustrated and impressed.

"Every single one he threw me had some sink or some run," he said.

Pirates manager Clint Hurdle likened the mix of power and movement a "gift from God." One Hicks and the Cardinals are still trying to harness, both on the field and off.

Hicks was invited to big league camp for the first time in spring training, only to find his initial stay short-lived after he had issues getting to meetings on time, something Hicks called "a learning experience" when St. Louis brought him up in late March. Though Hicks was impressive from the jump, it looked like he would start the year in the minors.

Then he made an emergency Grapefruit League start in place of Adam Wainwright against the Nationals on March 25 and held a lineup that featured nearly all of Washington's regulars to one hit over four innings. It was the kind of outing that left the Cardinals with little choice. Hicks' stuff was so good, sending him down seemed sort of pointless.

"If I didn't do well that day, if I didn't pitch the way I pitched, I wouldn't be here," Hicks said.

Getting to the majors is one thing. Sticking around is another. Save for a bumpy appearance against the Phillies on May 17 when he gave up three runs without retiring a batter, Hicks has been dominant. Opponents are hitting just .161 against him. Though he only struck out one in 2 2/3 innings against the Pirates over the weekend, he showed the ability to turn hitters' timing into a hot mess.

"The swing and misses are going to come, there's no question about it," Matheny said. "We're going to need as many bullets as he has and get him on the mound as often as we can."

Provided his body holds up under the strain. Though that's the weird part. Hicks doesn't look like he's giving max effort on the mound. The ball explodes out of his hand anyway.

The "little" 6-foot-2, 185-pound teenager from Houston who hit 90 on the gun when the Cardinals grabbed him with a supplemental third-round pick in the 2015 draft has added 25 pounds of muscle and 10-15 mph of velocity. Can he go higher? Maybe. That's part of the fun. Hicks never thought he'd top 100. Some days that's at the bottom of his range. Buckle up.

"I just try to get a little more from my legs and throw hard," Hicks said. "Hard, hard."