After nine years, 219 saves and one World Series championship in Boston, the 31-year-old right-hander was in the opposite bullpen for the first time since agreeing to a four-year, $50 million contract with the Phillies in November.
He didn't have to wait long to make an impact, coming in to pitch the ninth and save the Phillies' 6-4 win. He's now 12-for-12 in save opportunities this season.
"I've been looking forward to this since the day I signed here -- facing old teammates, bragging rights," Papelbon said while sitting in the Phillies' dugout. "It's like, you play with your brother in the backyard for so many years and you want to have those bragging rights. I don't want to have to hear from [Dustin] Pedroia or somebody like that -- text message or something like that. I want to be giving it to him. It will be fun, though."
At least, it looked like Papelbon. From time to time, he would lapse into the third person when talking about his alter ego, Cinco Ocho, a reference to both his uniform number and a play on NFL wide receiver Chad Ocho Cinco, nee Johnson.
Would he feel any different if he takes the mound against his former club?
"I don't think it will be," said Papelbon. "I'm just going to go out there and let Cinco take over, man. I'm not really worried about it."
Does Papelbon have an advantage over Red Sox hitters because of his familiarity with them or vice versa?
"Cinco always has the advantage," said Papelbon. "Whatever he does, he don't know how he do, he just do. He's always got the advantage. Never underestimate Cinco Ocho. It's 10-to-1 odds. Don't ever bet against him."
Will he be relieved to get his first appearance against his ex-team over with?
"No, man," said Papelbon. "Cinco don't feel that kind of pressure. Cinco's got ice water in his veins."
If Friday's game was being played in Boston instead of Philadelphia, what kind of reception would he receive?
"[Cinco would] probably like it more," said Papelbon. "That's just how it is, you know? It's just what he does. ... I think Pap would get a really good reception. Cinco, I don't know what kind of reception he'd get."
For most of his 10-minute pregame session with the media, though, he appeared as himself and he was jovial throughout.
The Red Sox hitter he'd most like to face is David Ortiz -- except that he referred to him as "Big Sloppy," even though Papi has lost 30 pounds since last season.
"Just the fact that if he gets me, I won't ever be able to say nothing to him, but if I get him, I'll always be able to say something to him," said Papelbon. "That's my man."
Ortiz responded with a laugh.
"As long as he don't make that face," said Ortiz. "Just look at him when he's pitching. You tell him two things. He's not going to throw fastballs by me, No. 1, and he better not hang that splitter. Let him know."
As it turned out, Ortiz pinch-hit in the eighth.
"I was kind of keeping track of that a little bit, but when it comes down to me getting ready to get into the ballgame and getting locked in and getting on the rubber to start warming up, that kind of all goes out the window," Papelbon said afterward.
He expressed mock outrage when the fact that Boston didn't make a formal contract offer was raised.
"You asking me that question? I don't know that answer. You've got to ask somebody else that question," he said, grinning.
Papelbon played it for laughs when asked about adjusting to National League hitters, insisting he simply followed the advice he got from Phillies bullpen coach Mick Billmeyer.
"I've probably asked him a lot of dumb questions," Papelbon deadpanned. "I've got a state education, so I'm not that bright.
"The biggest difference is the way the game is played. I'm home in two-and-a-half hours. In Boston, I'm pitching at midnight. I can't tell you how many times I turned around at Fenway Park and saw 12:02 or 12:03 [a.m.]."
All kidding aside, Papelbon also made it clear how much his time with the Red Sox meant to him.
"I'm proud of the championships we won there," said Papelbon. "I'm proud of being part of an organization that I felt like taught me how to play in the big leagues. I'm proud of playing for a manager in [Terry Francona] who taught me how to be a man, taught me how to accept failure, taught me how to accept winning. I mean, A to Z. I could sit here and talk all day about it, but for me, it's a lot of good memories and a lot of good people that surrounded me."
After the game, however, Papelbon was almost somber. No, he said, it didn't seem any different facing Red Sox hitters. No, he didn't feel any differently.
"There was a little extra buzz in the ballpark," said Papelbon. "Maybe [because] it was a weekend game or something like that. Other than that, no."
Coincidentally, Daniel Bard started against the Phillies on Friday night. Many, including Papelbon, assumed it would be Bard who would inherit the closer's role if he left. Alfredo Aceves has taken over the role since Andrew Bailey is on the disabled list and is 8-for-10 in save opportunities.
Papelbon wasn't ready to start exercising his bragging rights yet.
"We've got to win the series. We've got to take care of the business at hand," he said. "We've been on a good little streak here. We've got to keep this train rolling."
Paul Hagen is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.