Carlos Martinez has become the ace of the Cardinals while having to deal with the shocking death last October of his best friend, former St. Louis slugging prospect Oscar Taveras.

ST. LOUIS—Carlos Martinez wasn’t sure he could pitch. It was a fluke of the schedule that his name was on the lineup card, a byproduct of the Cardinals’ ever-fluctuating starting rotation. No one had counted backwards by five from May 31, not to ensure it would be Martinez’s turn, not to double-check that it wouldn’t.

Exactly one year before, the Cardinals' flamethrower had watched his best friend, the player known in their home country as “El Fenómeno,” launch a solo home run at Busch Stadium in his second major league at-bat. The ball ricocheted off a row of rightfield seats and landed in the St. Louis bullpen, just feet from where Martinez would warm up 365 days later, pitching through tears, his mind spinning. May 31, 2014 had unofficially been Oscar Taveras Day in St. Louis, the long-awaited moment when the Cardinals’ top prospect arrived in the big leagues—and a year later, the Cardinals and their fans celebrated Tavares again. Not a person in the building wished it were so.

May 31, 2015 was a celebration of life, but it was also a moment of mourning for the young man who passed away just 148 days after that first home run. Taveras, at home in the Dominican Republic, was driving under the influence and too fast near the town of Puerto Plata on Oct. 26, 2014 when his car ran off the road, killing him and his 18-year-old girlfriend.

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Martinez, who had been friends with Taveras since he was 11 years old, was with his family at a nearby resort. He’d had a feeling something bad might happen to the man he calls his brother, and just a day before the accident, he’d urged Taveras to join him. Taveras had declined, and in a night, Martinez aged a decade. When reporters traveled to the Dominican Republic for the 22-year-old’s memorial and funeral, it was Martinez who received them, who spoke publicly about his best friend, who vowed the tragedy would shape him for the better.

He said all the right things, and he meant them, but devastation can be a tricky shadow. Cardinals shortstop Jhonny Peralta, a 33-year-old veteran and native of Santiago, Dominican Republic, knew he should keep an eye on Martinez last fall and winter. The two talked on the phone constantly, and Peralta made the two-hour drive to Puerto Plata several times to visit his young teammate. As the winter progressed, Peralta says, he watched Martinez stick to his promise to stay on the straight and narrow path for Taveras while gradually improving his mindset.

“I feel like mentally he’s better and better,” Peralta says. “Everything with Oscar Taveras, it’s making him feel more mature. I don’t want to say it’s good to happen, but for some reason, this situation’s happened like that, and it’s made him better.”

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Once the wild card in the St. Louis clubhouse—the righty starter’s first two seasons in the big leagues saw his emotions run high on the mound—Martinez in 2015 is more subdued. "I've changed a little bit," he says through his translator. "I've dedicated more time to my family and gotten more focused on baseball." But his feelings about Taveras’s death are, if not processed, then processing—and publicly. That’s what happens when the entire world is asking, when Martinez must discuss the worst thing that’s ever happened to him with strangers who want—nay, expect—the most intimate, personal details of his relationship with a man gone decades too soon.

But on that unseasonably chilly afternoon of the last day of May, Martinez doubted himself. A pitcher, even one nicknamed “Tsunami,” is supposed to be cool, level, even-keeled; these are qualities Martinez has been working on all season. But as his team honored his brother, he could be none of those things, which made him wonder if he could even go through the physical act of pitching, much less do it well.

“When you’re there, and you’re in the bullpen … before the game, you can’t let it affect you either way,” says Carlos Villanueva, a veteran reliever who’s become something of a mentor to Martinez this year. “Because you can get over-motivated: I’m going to do great for him. And you’ll try to do … more than you have to.… If you get caught up in the good or the bad, you’re not being yourself.”

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And so Martinez built what Villanueva calls “his bubble.” He wiped his eyes and told his teammates: “Let’s do this for Oscar. Let’s do this for my brother.” In seven innings that day, wearing Taveras’s No. 18, which he adopted this season, Martinez pitched a one-hit shutout, striking out eight Dodgers. When he fanned Alex Guerrero to end the top of the seventh inning, Cardinals catcher Yadier Molina held onto the ball. As he approached St. Louis’s dugout, he flipped it to the Taveras family, who were seated along the third-base line. Only then could Martinez give in to the scope of the day.

With Adam Wainwright out for the season after tearing his left Achilles tendon in late April, the 23-year-old Martinez has quietly filled the vacant role of ace for a Cardinals team that has the best record in baseball. Since May 20, he has gone 4–1 with a 0.89 ERA. Overall, he is 9–3 with a 2.80 ERA, and he ranks in the top 10 in the NL in wins (third), winning percentage (.750; fourth), ERA (eighth) and strikeouts (10th). Opponents are batting just .184 against him and he averages 9.6 strikeouts per nine. After three rocky outings in mid-May in which he allowed 16 earned runs in 14 innings, it’s easy to wonder what changed, but the consensus around St. Louis’s clubhouse is simple: nothing. Martinez says his stuff has always been the same; it’s his focus that’s making the difference.

“When he had a couple bad starts, his body language got a little down, and we explained to him why that doesn’t work,” Villanueva adds. “You’ve just got to keep a steady personality all the way across. These are things he’s going to learn with time.”

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To watch Martinez pitch is to see a veritable mime show of grimaces and smirks, perhaps an errant smile after a 96-mile-per-hour fastball. There are moments, too, when he seems about to explode with emotion, when he has to step off the mound and deflate. But those episodes are fewer with every start, and Villanueva has drilled into his mentee the value of not giving opponents any extra ammunition, be it a grin they want to erase or a groan that fuels their motivation. Keep the theatrics in the clubhouse, Martinez has learned, and so he dances his way into his uniform, butt shaking, head bobbing, twitching as much of the hot-blooded Carlos as he can out of his system.

There are still moments in the dugout when Martinez turns to say something to Taveras. On the mound, his mind sometimes drifts to his old friend and then back to the game, because focus only goes so far, and for Martinez, baseball is so tangled up with Taveras that it’s hard to separate the two. When the lines blur, he calms himself with three words: Just keep living. And so Martinez cries and he steadies. He builds his walls and tears them down. He mourns and he dances.