Jayson Werth, right, is chased down by teammates after his game-winning single. (Toni L. Sandys/The Washington Post)

By the time the Washington Nationals caught up to Jayson Werth, the oldest of their bunch, they had chased him out into right field, hundreds of feet from where Danny Espinosa had just scored the winning run in their 5-4 victory over Philadelphia — and what felt like miles away from where Phillies third baseman Maikel Franco’s go-ahead home run had landed in the top of the ninth.

That Jonathan Papelbon gave up a run in a tie game in the top of the inning did not matter anymore. He, too, charged out to right field after Werth, who said in his postgame television interview that he knew he was in trouble when the “D.C. strangler” headed his way. There were the Nationals, jumping for joy in the middle of right field, their scars long since stitched up with smiles — 15 games over .500, 4 1/2 games up on the New York Mets in the National League East.

How did they get there?

They opened up a three-run lead in the first two innings Sunday. Michael A. Taylor, starting for the second straight day, this time to give Ben Revere a rest, singled to lead off the game. He has a hit in 14 straight starts.

Werth and Daniel Murphy walked behind him. Ryan Zimmerman and Wilson Ramos hit sacrifice flies. An inning later, Espinosa homered for the third time in four games. He has 11 home runs this season, tied with Murphy for second among Nationals. Bryce Harper, who did not start the game Sunday, leads with 13. But Espinosa’s biggest at-bat would come later.

Meanwhile, Joe Ross allowed three runs in seven strong innings, struck out eight and, for the first time all season, did not walk a batter — the kind of performance that has lifted the Nationals repeatedly and helped give their pitching staff the third-best ERA in the majors.

Sammy Solis threw a scoreless eighth, the first time he has been used in what could be considered a setup role. Then came Papelbon, in a tie game in the ninth at home, as conventional baseball wisdom suggests he should.

He hung a 2-2 slider to Franco. Franco hit it out.

“My opinion, most major league baseball players should hit that ball out,” Papelbon said. “It was a very poorly executed pitch.”

How did the Nationals get here, dancing around their outfield? With 16 saves in 18 chances from Papelbon, who has endured adventures in several others. One game does not a crisis make, and something about his former team changes him, it seems, because out of the four saves he has blown since being traded from Philadelphia to Washington last year, two have come against the Phillies. Papelbon has lost three games as a National, two to Philadelphia. He has allowed two home runs and nine earned runs in 24 2/3  innings.

“I feel like I’ve been as successful as I have been in many other years,” Papelbon said. “I haven’t been that great in tie ballgames this year, but when my number’s called for save situations, you know . . . ”

Ultimately, it did not matter Sunday. With one out in the bottom of the ninth, Nationals Manager Dusty Baker pinch-hit Harper, who was supposed to have the day off. He grounded to the right side, where Phillies second baseman Cesar Hernandez threw high to first base. Harper was safe. Tommy Joseph appeared to come off the bag and said later he could not find it with his foot. The Phillies challenged the call. With a potential rally in the balance, bench coach Chris Speier was on the phone with Nationals personnel watching video. Baker looked over and rotated his hand to indicate a so-so prognosis — not exactly what he had hoped to see, he admitted afterward. The call was upheld.

Then came Espinosa, who has always shown power but always battled for contact. He found himself in a 1-2 count against Phillies closer Jeanmar Gomez, then fouled off two tough pitches. Then he looped a single into left.

“He’s been working on that. We keep stressing to him that when you get in a hole, you’ve got to put it in play,” Baker said. “And if you put it in play, anything can happen.”

Baker pinch-hit next with Revere. He lined out. Baker pinch-hit Clint Robinson for Taylor with two outs and the tying run at second. He walked. Then came Werth. Early-evening shadows had been creeping toward the mound for some time, and they left Werth “struggling to see until about the third pitch,” he said later. How did he end up bouncing in right field a few moments later?

“I think he ran a heater back over the plate a bit,” Werth said. “Just smacked it up the middle.”

Baker clapped his hands and stomped his feet. Harper fist-pumped and jumped around as Espinosa scored. Then the whole dugout charged after Werth, who has seven career walk-off hits.

“We’re resilient. We’ve been resilient,” Werth said. “Same team we’ve had, really. We’ve added pieces, we’ve lost some guys and added some guys, but the core of this team has been here. We’ve been a resilient bunch.”

Baker has said he checks the boxes off in his mind — 10 games over .500, 12 games over .500, and so on. By the time Tanner Roark caught Werth by the collar and his teammates swarmed around him, the Nationals had hit Baker’s most recently identified target — a 15-game cushion.

“Next step,” Baker said afterward. “Twenty games over.”