The first lesson came from Ramon Ramirez, a 36-year-old reliever with more than 400 games of major-league experience. Be ready at all times, Ramirez would say, because you never know when the phone will ring or what the voice on the other end might tell you.

Seranthony Dominguez had already found that out.

It was the end of last season, and Dominguez, a hard-throwing pitching prospect, was looking forward to making a few starts in winter ball back home in the Dominican Republic. But the Phillies had other plans. They wanted to turn him into a reliever, and winter ball was going to be his first classroom.

So, Dominguez joined Gigantes del Cibao, a team based two hours east of his hometown of Esperanza, plopped himself next to Ramirez in the bullpen, and soaked up as much advice as possible about succeeding in a role that seemed on the surface to be a demotion.

It wasn't, of course. The Phillies signed Dominguez as a 16-year-old in 2011, and over the next six years, they watched his fastball velocity climb into the upper 90s. He threw a nasty slider, too. And rather than waiting for his change-up to continue to develop, the Phillies figured Dominguez could reach the majors more quickly if he moved to the bullpen and primarily used his two best pitches.

Sure enough, after 13 innings at double-A Reading and only 3 2/3 at triple-A Lehigh Valley, Dominguez was called up Monday. He made his major-league debut a few hours later, punctuating a perfect eighth inning by striking out Evan Longoria in an 11-0 victory over the San Francisco Giants.

"It's a moment I will never forget," Dominguez said.

Just like he won't forget the tips he picked up last winter in the Dominican, where it wasn't particularly smooth sailing for the novice reliever.

Dominguez made seven appearances for Gigantes and gave up four earned runs on eight hits in 7 1/3 innings for a 4.91 ERA. He struck out eight but walked nine. And he learned what Ramirez described as the key to surviving life as a reliever: Throw strikes, as many as possible.

"He came to understand that, as a starter, you've got innings to work with. As a reliever, you don't," Gigantes manager Pedro Lopez said by phone Tuesday. "I thought he learned the importance of going out there and making sure that he worked ahead. When he did, he was lights out. I mean, his stuff was untouchable. But when he didn't, that slider didn't play, the change-up didn't play."

Dominguez pounded the strike zone through the first month of the season in the minors. In 16 2/3 innings between Reading and Lehigh Valley, he struck out 21 and walked only three.

It was more of the same in Dominguez's first major-league appearance. Of his 17 pitches, 12 were strikes. Dominguez threw first-pitch strikes to both Nick Hundley and Brandon Belt, and after falling behind 3-1 to Longoria, he got him to foul off a 98 mph fastball before freezing him on an 87 mph slider.

"He's got an electric fastball," said Lopez, a minor-league manager in the New York Mets organization. "If he's able to command that pitch in the strike zone, I think he's going to get major-league hitters out. We saw him do it in the Dominican last winter."

Dominguez acknowledged that he wasn't quite sure how to handle the news that he would be moving to the bullpen. After all, most pitchers prefer to be starters.

But Ramirez helped Dominguez realize there's little sense in worrying about his role. Pitch well and you'll make it to the big leagues.

"He said, 'You don't know when they're going to call you up. You've just got to be ready,' " Dominguez said. "It doesn't matter if you're expecting it or not. You have to be ready because that moment is going to happen in the moment you least expect it."

Dominguez wasn't expecting it to happen this quickly. But he impressed Phillies manager Gabe Kapler in spring training. And when Kapler attended a game in Reading last month, he came away raving about Dominguez' electric stuff and calm demeanor.

When Kapler announced Monday that the Phils had promoted Dominguez, he said he won't be shy about using the 23-year-old in high-leverage situations. Asked to describe Dominguez' role, Kapler said he would "take down meaningful innings." Before long, it won't be surprising if Kapler uses Dominguez in save situations.

"The thing that I find most impressive about him is his composure and his maturity and his mental readiness," Kapler said. "Those are the things that stood out in spring training and continue to stand out."

Kapler had to laugh, then, when Dominguez coolly returned to the dugout after the eighth inning Monday night.

"I asked him if he was nervous, and he said no," Kapler said. "I said, 'Are you sure? Not even a little bit?' He said, 'No, I wasn't nervous out there. I was just really excited.'"

Said Dominguez: "That's my personality. It is a moment I have been waiting for. It is something I have been getting ready for mentally and physically. I just took it as, 'Well, this is my time. Now I have to show them that I'm ready.' "

After all, Ramirez told Dominguez to always be ready.

It seems he listened.