Ivan Nova credits Mariano Rivera for helping him improve his focus. Reuters

PORT CHARLOTTE, Fla.—Two years ago, Ivan Nova was in the midst of a 16-4 season, and flying high. He had overcome a demotion to the minors earlier in the season, and was sure that he was in the majors to stay.

He was winning games, strutting around the clubhouse—and falling into bad habits on the mound as the powerful Yankee offense bailed him out of some poorly pitched outings. Nova, now 26, said the wins were what mattered, not his ERA, and said he was making good pitches—at the same time manager Joe Girardi said he was making mistakes.

That was when Mariano Rivera took it upon himself to pull Nova back into line. He told Nova that if he didn't get back to proper habits, he'd be back in the minors.

"He told me, if you don't do what you're supposed to do, you're going to get sent down," Nova said. "That means you're not doing everything necessary to stay. So you've got to keep doing more than what you're doing.

"When he told me that, I couldn't even look into his eyes," Nova said. "You feel bad. If Mariano Rivera tells you you're going to be sent down, you're not doing something right."

Like the apocryphal Roman slave tasked to walk behind Rome's conquering generals and whisper, "All glory is fleeting," Mariano Rivera takes it upon himself to remind the Yankees' developing young pitchers that they are always a hairsbreadth away from failure. That no matter how good they think they are, other players are working harder to beat them.

And because he is Mariano Rivera, the players are compelled to listen. As Nova did then, pitching well for the rest of the season.

"You want them to use their abilities, and he has a lot of abilities. You're going to make sure they do whatever is right and they don't waste it," Rivera said.

In his final season, Rivera is part closer, part mentor, to the young Latino pitchers in Yankee camp; a stern taskmaster who tells them that they are not living up to their potential. He has taken a special interest in Nova, whom he sees as a talented pitcher who needs to focus.

"He's young still, so we just have to reinforce that we need him," Rivera said. "We need everyone here, and our kids come from the Dominican, Panama, Venezuela or whatever. We have to make sure they stay on top of their game."

After righting his ship in 2011 and finishing the season strong to become New York's No. 2 starter in the playoffs, Nova scuffled through a sub-par 2012, where the Yankee brass often said he was losing focus. When Nova arrived in camp this season, Rivera let him know that the time for lollygagging was over.

"One thing that he told me when I saw him here this year was that he was going to be on top of me, that whatever happened to me last year, we cannot let that happen again," Nova said. "When a veteran like that motivates you that way, it means a lot."

Nova is locked in a competition with David Phelps to be the team's fifth starter. So far, he has taken Rivera's words to heart, throwing nine innings of one-run ball over three spring starts. Nova held the Tampa Bay Rays scoreless over four innings Tuesday, working out of several jams with a resolve that impressed his manager.

"The thing that I liked most was he got out of the inning with first-and-third and nobody out," Girardi said. "Those are things you need to be able to do to be a successful pitcher."

If Nova falters, Rivera will be on him. Rivera's style, Nova said, is to tell a young pitcher that he's doing something wrong—but not what that is. Nova said Rivera forces him to figure things out for himself.

Rivera said that the late Steve Howe, the former drug abuser turned evangelical Christian, was a huge influence on his early career, keeping the young Rivera in line when he would start to fall into bad habits. Rivera, who said he wants to work with minor leaguers when he retires after this season, is still trying to pay that forward, as he is doing with Nova.

Howe "always was there, making sure I was doing the right things and motivating me always to do what is right and to go with everything that you have," Rivera said. "I will never forget that, and that was '95. Now we are 2013 and I'm trying to do it for the others."