Derek Matlock knew as soon as he saw it.

Matlock was coaching at Texas State University in 2009 when a few players talked him into driving to west Texas to watch the bullpen session of a pitcher who had been cut from his junior college team. At first, there wasn't anything striking about the tall, skinny right-hander with hideous numbers at Grayson County College and a reputation for not being receptive to coaching.

That's when Carson Smith said the words that changed his career.

"He goes, 'Coach, let me throw one from three-quarters,'" Matlock, now the pitching coach at West Virginia, recalled in a recent phone interview. "I was like, 'All right,' so he did. And after seeing one from three-quarters, I was like, 'Oh baby, this guy's gonna be a dude.' I was pretty fired up."

If Matlock hadn't seen Smith, another Division I pitching coach probably would have. Then again, Smith went undrafted out of high school and only had offers from other junior colleges.

And considering Smith's indirect route to the big leagues, there was something fitting about the winding path to his first appearance for the Boston Red Sox on Tuesday night.

After missing the first month of the season because of a flexor mass strain in his right forearm, Smith was activated from the disabled list and tossed an easy, breezy nine-pitch seventh inning in a 4-1 loss to the Chicago White Sox. He got Jerry Sands and Dioner Navarro to ground out, then struck out Austin Jackson on a nasty slider.

"It's great to be back," Smith said, as the Red Sox and White Sox continue their three-game series on ESPN's Wednesday Night Baseball. "I've wanted to be here for the last month. Just to go out there and get one out of the way, it was good."

With his unique arm angle and strikeout ability, Smith figures to boost a bullpen that appears to be one of the Red Sox's strengths. Acquired in a December trade that sent lefty Wade Miley to the Seattle Mariners, the 26-year-old gives manager John Farrell an alternative to 41-year-old setup man Koji Uehara and overused Junichi Tazawa, who gave up two runs in the eighth inning Tuesday.

"I coached Jake Arrieta at TCU and Corey Kluber in summer league, so I've had some great guys. And I always told everybody when Carson left, 'I think that guy might be the best guy I've ever had.' They're like, 'Shut up.' But I swear to God, he might be. He was just a special kid." Derek Matlock, Carson Smith's pitching coach at Texas State

But what if Smith hadn't lowered his arm during his tryout for Matlock? What if he hadn't wound up at Texas State? What if?

"I always knew there was going to be baseball in my future," Smith said. "However long it lasted, I wasn't too sure. I've always pushed myself to prove others wrong. I was cut from a junior college team. If I didn't hit a wall there, I don't know what was going to stop me."

After years of throwing from different angles, Smith was coached at Grayson to use an over-the-top delivery and leverage his height (6-foot-6) to gain downhill action and greater velocity, an approach that contributed to underwhelming results in the fall of 2009 at Texas State and led Matlock to encourage Smith to stick to the lower arm slot.

Sure enough, Smith posted a 2.52 ERA and 223 strikeouts in 218 innings over the next two seasons.

"All of a sudden, he was slinging it with sink and command, his breaking ball was better, his changeup was better," Matlock said. "I was like, 'We've got a monster here.' That arm slot, it happened in one bullpen and his life changed."

Indeed, Smith's slider from the right side is nearly as overpowering as New York Yankees reliever Andrew Miller's is from the left. According to data from Brooks Baseball, Smith got swings and misses on 42.89 percent of the 464 sliders he threw last season compared to Miller's 48.37 percent on 521 sliders. One veteran talent evaluator from a National League team compared Smith to former Mariners and Yankees reliever Jeff Nelson, who was known for his "frisbee slider" from a three-quarters release point.

But it's also fair to wonder if Smith is at greater risk of injury because of the lower arm angle. Perhaps that's why the Mariners were willing to move a late-inning reliever with so much upside. Another rival talent evaluator said he typically gives Smith a "caution" designation in his scouting reports, but added he wouldn't have been concerned about trading for him.

Even Matlock said he often had to remind Smith not to drop down so far that his elbow was lower than his shoulder when he released the ball.

"For the most part, it feels natural. It's not forced," Smith said. "If I tried to throw over the top, that would be forced. Right now, I'm just running with it. It feels good."

Last year, his first full season in the big leagues, Smith notched a 2.31 ERA in 70 appearances and 13 saves after stepping in for ineffective Mariners closer Fernando Rodney.

Although the Red Sox intend for Craig Kimbrel to get the lion's share of save opportunities, it's helpful to have another power arm at the back of the bullpen capable of closing out games, especially in an age when power bullpens are all the rage. Just look at the two-time defending AL champion Kansas City Royals.

"I coached [Chicago Cubs ace] Jake Arrieta at TCU [Texas Christian University] and [Cleveland Indians ace] Corey Kluber in summer league, so I've had some great guys. And I always told everybody when Carson left, 'I think that guy might be the best guy I've ever had,'" Matlock said. "They're like, 'Shut up.' But I swear to God, he might be. He was just a special kid."

Better late than never, the Red Sox are ready to find out how special.