Jonathan Papelbon doesn’t buy it.

No matter the thought that formally designating a set-up man is crucial to a bullpen’s success, for how it creates roles and sets expectations that players — especially relief guys — can cozy up to, Papelbon isn’t even listening.

“Nah, man. That doesn’t matter,” he said after the Phils 9-7 win over the Marlins Tuesday, of which a gut-check eighth inning was a big part. “It’s everybody down there.”

Maybe. But everybody still makes it nobody for the Phillies, who’ve yet to officially tap someone to serve as the bridge between middle relief and the end of the sentence.

“That’s irrelevant, really,” he said.

Papelbon may be right. According to the Elias Sports Bureau, the Phillies team ERA in the eighth inning since August 23 is a 1.00, tied for the best in baseball.

The significance of the date? That night, Phillippe Aumont, the Phils rookie 23-year-old Canadian with 98 m.p.h. stuff, made his big-league debut. Since, he and Antonio Bastardo have been Manuel’s seeming go-to set-up men.

All but one of Aumont’s appearances have come in the eighth, the other being Sept. 3, when he logged his first career save in the ninth.

He’s allowed just one run in eight appearances for a 1.23 ERA.

Nine of Bastardo’s last 11 spots have come in the eighth, and he’s allowed just one run in his last 13 eighth-inning appearances.

His last nine times out, Bastardo has allowed just one run.

In other words: Manuel’s, counterintuitive as it may be, is working.

It wasn’t before. On the season, the team’s eighth inning ERA is 4.42, a microcosm of an altogether atrocious relief staff that, for a while, ranked worst in baseball by just about every measure.

Matter of fact, if you go back to Aug. 12, just 11 days before Aumont’s debut, the team’s eighth inning ERA was a 5.59, fourth-highest in the game according to the Elias Sports Bureau.

Still, the question now is that of an age-old debate over two schools of thought: (1) If it ain’t broke, don’t fix it, (2) Just because something works well doesn’t mean it can’t be better.

“He was big,” Manuel said of Aumont, who last night fanned two to pad a two-run lead that, after the Phils allowed seven runs in the seventh to cut it to one, didn’t seem so sure-thing.

After allowing the first two batters he faced to reach and a sacrifice bunt from the next, Aumont settled in nicely for two quick Ks, one on Jose Reyes to end the inning.

Pressure situation, that was, with runners on second and third. But Aumont proved a gamer.

“That was really good for us and him,” Manuel said. “That’ll bring confidence in him. Sometimes that’s what it takes. Takes some experience to get into the game, takes coming back and pitching when you get behind in the count. He did a good job.”