MLB

ROOK’S GRADUATION DAY

ATLANTA – Mike Pelfrey instantly recognized the sequence of signals from Paul Lo Duca, saw that his catcher wanted him to throw a slider, and understood that of all the small, imperceptible steps that transform prospect into pro, bush leaguer into big leaguer, he was about to take one, right here, bottom of the fifth inning, 45,611 Turner Field Tomahawkers yelping in his eardrums.

Lo Duca wanted a slider.

A few months ago, during Pelfrey’s often lurid and occasionally terrifying first two tours with the Mets, there is no way Lo Duca would have called for a slider right now, and even less of a chance that Pelfrey would have agreed to throw one. The Braves already had a run in, the tying runs were on base in a 3-1 game, he had a 3-and-2 count on Kelly Johnson.

And Chipper Jones was lurking on deck.

“The way he was throwing,” Lo Duca would say, “I had confidence that he could throw exactly what he needed to throw there, get us out of the inning.”

More important, Pelfrey felt the same way. Earlier in the season, as Pelfrey endured 10 excruciating starts that yielded an 0-7 record and a 5.92 ERA, there always seemed to be one inning that sent him flying, the way one tough par-5 can ruin a perfectly enjoyable round of golf. Often, Pelfrey would settle down and start collecting outs, but the damage would already have been inflicted.

And the Braves, they were looking to inflict some now. Already there had been signs. The Braves had mounted this rally without a hit thanks to two walks, a hit batter and a sacrifice fly. After pounding the strike zone for four innings, Pelfrey had lost radio contact with it now. And Turner Field smelled blood.

“I’d gotten careless,” Pelfrey would admit. “And you can’t get careless, not when you’re playing a game that’s this important.”

Still, Lo Duca believed in what he’d seen across the first few innings.

“He was unhittable,” the catcher said, “and was throwing as well as I’ve seen any of our guys throw this year.”

The fastball would have been the safe call. A grooved fastball also could have given the Braves a 4-3 lead. Professional pitchers aren’t afraid to throw their breaking stuff in these spots.

Lo Duca flashed the signs. Pelfrey nodded. Slider it would be.

“Sometimes,” manager Willie Randolph would say, “when young pitchers struggle, it’s almost a blessing in disguise. They learn what they need to do to get better and succeed up here.”

It wasn’t a strike, as it turned out, but it sure looked like one to Johnson as it approached, it looked like the kind of fat fastball Pelfrey would have fed him three months ago, and it wasn’t until Johnson had already committed to swing that the ball took a dive south, and a quicker turn in. He missed the ball by a foot. The crowd groaned. Lo Duca rolled the ball back to the mound.

And Pelfrey, maybe for the first time, felt like a major-league pitcher.

“I knew, coming in here, if I help this team in the middle of a pennant race, maybe I could start forgetting what happened the first time I came up this year,” Pelfrey said. By now he was showered and smiling, satisfied with the six innings and 99 pitches he threw, and by the one run and one hit he allowed, and by taking a quantum leap toward justifying the lofty place he’s held in the Mets’ plans the past two years.

“This,” he said, “could turn my whole year around.”

It certainly has helped put a roadblock up on the downward slope upon which the Mets were skidding just 48 hours ago. Turner Field has never been an antidote for anything that ails the Mets, yet in the two days they’ve spent here so far they’ve already gotten Pedro Martinez back in the fold, gotten John Maine back on a winning track and now gotten their prized ace of the future his first big-league victory in exactly 408 days.

All in all, not a terrible visit so far.

michael.vaccaro@nypost.com