PHILADELPHIA – PJ Poulin wasn’t part of the Tigers’ trade package for Kyle Finnegan, but he might as well have been.

When Detroit acquired Finnegan from the Nationals at the trade deadline for minor leaguers Josh Randall and R.J. Sales, another transaction was necessary to clear a 40-man spot for the veteran reliever. The odd man out wound up being Poulin, who was pitching well at Triple-A Toledo but was deemed expendable and thus was designated for assignment.

The Nats, of course, swooped in and claimed the 29-year-old left-hander off waivers, then surprised him by sending him not to Triple-A Rochester but straight to Washington to join a big league roster for the first time in his career.

Poulin, an 11th-round pick of the Rockies in 2018 out of the University of Connecticut, was stunned just to be in the majors. Three weeks later, could he have believed he would find himself on the mound in the bottom of the ninth at Citizens Bank Park, trying to close out a one-run win in front of a sellout crowd of Phillies fans?

“Uh, I mean … no,” he said with a laugh after contemplating how ludicrous that notion would have sounded at the time. “This has been like the best three weeks of my life.”

It’s hard to argue that point. In recording the final six outs of Friday night’s dramatic 5-4 win over the Phillies, Poulin capped off an impressive opening act to his big league career.

He has now pitched in 10 games for the Nationals, totaling 10 innings of work. He has allowed only two runs on six hits, striking out 12 while walking four. And thanks to his efforts Friday night, he now owns a major league win.

With Jose A. Ferrer and Cole Henry unavailable after pitching the previous two days, Poulin was given the bottom of the eighth, with the Nats trailing 4-3 at the time. He actually faced three straight right-handed batters in Alec Bohm, Nick Castellanos and Harrison Bader but thrived, retiring the side with strikeouts of both Bohm and Bader.

Had his teammates gone down quietly in the top of the ninth against Jhoan Duran, Poulin’s night would have been over, just like the game. But when he returned to the dugout after the quick eighth, he was told to keep himself warm because he’d be right back out there for the ninth if the Nationals somehow rallied.

“Oh, he knew,” interim manager Miguel Cairo said. “We didn’t have Ferrer. We didn’t have Cole Henry. He knew he was going in there.”

So when Dylan Crews and Daylen Lile teamed up to produce the tying and go-ahead runs off perhaps the most dominant closer in baseball, Poulin indeed found himself going back to the mound for the bottom of the ninth in what amounted to a save situation, even though he officially was now in line for the win because he had pitched the eighth.

Poulin got to face two lefties this time. He induced a popup out of Bryson Stott. He got the right-handed Trea Turner to go fishing at a changeup for a big strikeout. And before Bryce Harper could get fully ready in the on-deck circle, he got MVP candidate Kyle Schwarber to line out to right on his first pitch, ending the game and setting off an unexpected celebration at the middle of the diamond.

“Just pure joy,” Poulin said. “I’m a pretty competitive guy, like probably most of the guys in here. It felt really good to get that final out.”