Lucas Giolito’s potential is so conspicuous that it’s changed the discussion from what he will bring to the Washington Nationals’ starting rotation to when, exactly, he will bring it.

Stature and demeanor and raw talent rarely combine as they have in Giolito, who Baseball America and MLB.com agree is the top right-handed pitching prospect in the sport. His 6-foot-6 frame is the template for power pitchers. His composure on the field and poise off it resemble the traits of a 10-year veteran. And his biting, dropping, deceiving curveball comes along once in a blue moon.

But that confluence of assets brings with it a high-stakes fate: Players so perfectly molded for their craft turn out to be stars or disappointments, rarely something in between. High-90s fastballs and paralyzing curveballs cultivate attention. At 21, Giolito is handling it.

Teammates and coaches around him at his first major league spring training testify to his maturity. Giolito flashes smiles, is unafraid to toss out jokes and once admitted he liked a Justin Bieber song.

From the straight face he maintained as veterans pummeled him with sunflower seeds during an in-game interview to his weekly baking escapades that he’s been sharing on Twitter, all indications suggest Giolito is comfortable being himself despite the spotlight. He is not too eager for the hype, but he feels no need to hide from it.

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The attention “can be fun,” he said.” It can be cool to reach out to fans and see what they have to say.

“Then there’s a different side of it with the prospect rankings and stuff. It’s cool, but you don’t want to be a prospect. You want to be a big leaguer.”

It all just clicked

None of this pressure, and only a fraction of the attention, had converged on Giolito by early May of his sophomore season at Harvard-Westlake, a top prep school in Los Angeles. Until the day of a must-win game against highly ranked Crespi Carmelite High School, Giolito was all potential, but not yet a prodigy.

[Lucas Giolito strikes out the side in his first spring training start]

Giolito had always been the biggest kid on his Santa Monica-area teams, a hard-throwing behemoth so intimidating that his parents, Rick Giolito and Lindsay Frost, had to pull him out of Little League.

“By the time he was 11, he had already broken the hands of two catchers and ear-holed a kid, sent him to the hospital,” his father remembered. “He was throwing probably 75 miles per hour at 12 years old.”

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Giolito’s intimidation factor crumbled away from the field, undone by his goofy sense of humor and varied off-field interests. He was exposed to elite baseball in the hotbed that is Southern California, but was exposed to far more, too.

Rick Giolito acted briefly in shows such as “As the World Turns” and “Who’s the Boss” before becoming a producer, then switching to work producing video games, including those in the Medal of Honor series, for Electronic Arts. Frost acted, too, appearing in “Lost,” “CSI,” “Frasier” and other series. Her father, Warren Frost, had a recurring role on “Seinfeld.” Lucas’s uncle Mark Frost co-created the show “Twin Peaks.” Rick’s father, Silvio Giolito, was a two-time Olympian fencer.

“He’s been around all of this hullabaloo going on his whole life. It’s not new to him,” Rick said. “Plus, people start talking to you when you’re 14 and throwing 90.”

Giolito tried basketball and water polo. He took weekly golf lessons and played in junior tournaments. For six years he played French horn. But he focused on baseball, always aware of his unique talent.

“I was hoping he would make varsity by the time he was a junior. Maybe, maybe, the miracle of miracles would be if he could get a scholarship in college,” said Rick, a New York Mets fan. “But I thought that was a little far-fetched.”

Harvard-Westlake Coach Matt LaCour, now an athletic director at the school, pulled Giolito up to varsity his freshman year. He threw around 14 innings, his dad remembers, most of them undone by an unhelpful propensity to throw his fastball in the dirt. Still, that 90-mph stuff earned him some time to grow into it, so he ended up starting key games as a sophomore, struggling still.

“He was very upset about it,” Rick Giolito remembered. “I would tell him, ‘One day, it’s all going to click. Just be patient. It’s going to click.’ ”

It had not clicked by late April when, with his team in contention for a playoff spot, Giolito endured a painfully short start, plagued by poor command.

“I remember I was so distraught,” Giolito said. “I went home that night like, ‘Oh my god, I can’t throw strikes. I don’t know what I’m going to do.’ ”

A week later, Harvard-Westlake found itself needing a win against Crespi to make the playoffs. Giolito threw a complete-game one-hitter, struck out four and walked two. Harvard-Westlake pulled the upset.

“He had a hard time as a sophomore. That day, that game, it was a big game for our season,” Ethan Katz, then the Harvard-Westlake pitching coach, said. “He had had the ability; just the confidence hadn’t shown up yet. Once that game was over, the confidence took off.”

By the spring of his senior year, Giolito was hitting 100 mph in preseason outings, and no one could hit him. Scouts and general managers told him he might be the second overall pick in the draft, maybe even the first. At age 11, Giolito had announced to his parents that he would be a major leaguer. Now, he was close.

Then, in one of his early starts of that 2012 season, Giolito felt pain in his right elbow — trouble, though not a tear yet, in the ulnar collateral ligament. He stopped talking to scouts and executives. As other top prospects scribbled out pre-draft deals, Giolito wondered whether he might fall to the second or third round, whether he might be fulfilling that commitment to UCLA after all. He never heard from the Nationals before draft night. They chose him 16th overall.

“The Nationals took me out of nowhere. I hadn’t talked to them at all,” Giolito said. “I heard [Commissioner] Bud Selig say my name during the draft and that was the first I knew about it.”

[Spring training is a piece of cake for Lucas Giolito]

Giolito and his parents deliberated. Should he go to UCLA? Should he go join the Nationals? Though Giolito had not “completely blown out” the ligament, he figured he would probably need Tommy John surgery, a procedure in which doctors replace it with a tendon taken from elsewhere in the body. He and his family knew the Nationals’ track record working with pitchers with UCL tears, had seen what Stephen Strasburg and Jordan Zimmermann had done after their surgeries.

Giolito decided to go pro.

“We were going through what was an emotionally wrenching time with him getting hurt,” Rick Giolito said. “Him getting drafted by the Nationals was like a giant release. We just didn’t know. I was so happy for him. Everybody was happy for him.”

The future is now

When Nationals assistant general manager Doug Harris saw Giolito throw after his successful surgery in August 2012, he was struck by “the physicality of the man.”

“It was really a glimpse of what we see now,” Harris said. “You saw terrific angle to the fastball, terrific carry to the fastball, a legitimate swing-and-miss breaking ball, and probably the most surprising part was how quickly he showed some feel for a change-up.”

Giolito implemented his impressive arsenal while the Nationals watched carefully. He returned for 11 games in 2013 and struck out 39 in 36 2/ 3 innings of short-season and rookie league ball.

The next season, the Nationals limited him to work from April to August for Class A Hagerstown, where he went 10-2 with 110 strikeouts in 98 innings. Last season, the Nationals held Giolito out until May, which left Giolito — now feeling fully healthy — agitated to get going with Class A Potomac. He finished the season in Class AA Harrisburg, all the while impressing.

When Nationals Director of Player Development Mark Scia­labba invited Giolito to the Potomac Nationals’ “Hot Stove Banquet” last offseason, and told him it benefited charity, Giolito assented immediately.

“That’s the type of person he is. He’s not just about himself,” Scia­labba said. “He’s about the organization and doing what he can on and off the field.”

With his health intact and his game developing, the Nationals brought Giolito to his first major league camp this spring. Executives told him to be a “fly on the wall,” to soak up lessons from veterans like Strasburg and Max Scherzer.

“For being 21 years old, he shows a lot of maturity being here,” Scherzer said. “He’s got a sense of humor so he’ll blend in well with the clubhouse. He seems interested in learning the game and trying to think on the next level.”

Giolito may someday replace Strasburg, his fellow Southern Californian, as the “homegrown” ace at op the Nationals’ rotation. That day may come sooner than later, too, should Strasburg depart as a free agent next winter.

“You don’t want to be overbearing, but you don’t want to coddle him either,” Strasburg said. “I just try to do my thing, and when he has any questions or wants advice from me, I do my best to give some good advice.”

Giolito’s locker was a few stalls down from those big names in spring training, close enough to become one of the guys, close enough to elite big league pitchers to understand how far he has to go.

“You have to know how he’s leaning at the plate,” Giolito said. “Is he going after balls like this? Is he pulling off? Reading swings. You’re thinking about what pitch sequence is good against this hitter. It’s like a whole other level.”

His coaches stopped letting Giolito hit when he was a sophomore in high school. He hasn’t run the bases much lately. His bunting needs work.

Scialabba said Giolito must continue to improve his fastball command, hitting all four quadrants of the strike zone; learn to hold runners; and learn to pitch when he doesn’t have his best stuff — “the finer things,” as Scialabba called them.

[Key to winning NL East? “No mercy” for Braves and Phillies.]

Most pitchers Giolito’s age are trying to hone a second pitch, maybe add a third. Giolito spent parts of spring training outings trying all three of his in unexpected counts, and adding a two-seam fastball for a different look. Afterwards, he critiqued himself with a pitching coach’s insight. When he was unhappy with an outing, he said so. All spring there has been pressure, but Giolito always seemed far too busy being himself and doing his job — with media, with teammates, with coaches, and with fans — to notice.

“He doesn’t seem to get rattled much,” said Manager Dusty Baker, who had said repeatedly this spring training how impressed he was with Giolito’s pitching and presence. “But if I had that stuff, I wouldn’t be easily rattled, either.”