PHILADELPHIA — Heading into the bottom of the seventh inning, the Nationals seemed in control of Wednesday’s game. They executed most of their pitches. They made most of the right swings. And they had a sizable lead.

Yet, slowly but surely, things unraveled. The pitchers failed to execute. The Phillies made clutch swings in the final innings. And, ultimately, the Nationals fell 6-5 to the Phillies in extra innings.

It was nearly a different story. Cole Henry was one strike from earning the Nationals their second series win of the year. Then Edmundo Sosa hit a liner toward CJ Abrams. The ball kept carrying over the shortstop’s head. Sosa’s two-run single tied the game.

In the 10th, the Nationals couldn’t score against Jhoan Duran. Henry allowed a game-winning single to Justin Crawford in the bottom of the frame. Henry resorted to standing on the mound and watching as the ball rolled in the grass.

“We’re going to face those guys a lot throughout the year,” Henry said. “It’s good to kind of get in those situations early, because it’s going to happen a lot during the season. Just hope the outcome is different next time.”

The Nationals (3-3) entered Wednesday with a difficult matchup: Philadelphia’s recently extended southpaw ace Cristopher Sánchez, the National League Cy Young runner-up.

In practice, the game plan against Sánchez is simple. Hitters know he wants swings at the bottom of the strike zone to generate groundouts and strikeouts. Their plan is to avoid swinging at those pitches and take advantage of mistakes up in the zone.

Executing that game plan is not so easy. But the Nationals did an admirable job. They laid off bad pitches. They fouled balls off. They extended at-bats.

The Nationals chased only 22% of Sánchez’s pitches. They also made him work. Washington hitters fell behind 0-2 in five at-bats against Sánchez but generated three walks.

Philadelphia scored a run in the first. Washington responded with a run in the second. The Nationals ran up Sánchez’s pitch count. By the sixth inning, the Phillies turned to the bullpen. The Nationals offense took advantage.

Drew Millas hit a two-run, two-out single into center field to drive in Jacob Young. The following inning, Daylen Lile beat out an infield single with two outs. Joey Wiemer singled. Then Abrams launched a three-run homer to give the Nationals some cushion. But that didn’t last.

“No one wants to lose,” Abrams said. “We fought, played hard. I would say we played pretty good. Just didn’t turn out the way we wanted.”

The Phillies clawed back, giving a Nationals bullpen that performed well to open the season a reason to sweat.

Solo homers from J.T. Realmuto in the seventh and Bryce Harper in the eighth cut the lead to 5-3. Then Philadelphia brought Kyle Schwarber, the tying run, to the plate with a runner on in the ninth.

Manager Blake Butera used every trick in his book to salvage the game. He brought in PJ Poulin, his lefty specialist, to face Schwarber and Harper.

“I thought we fell behind [in the count] there a little bit at the end of the game,” Butera said. “Those guys pitched their tails off against a really good lineup. ... I think just, if you pick one thing, it’s probably just getting ahead of hitters a little better.”

One day prior, Butera used Poulin as an opener against the same section of the Phillies’ lineup. He executed to perfection against Schwarber and Harper. On Wednesday, Poulin walked Schwarber and Alec Bohm to load the bases, forcing Butera to turn to Henry with the bases loaded and two outs.

“Just attack them more,” Poulin said. “That’s what I did good yesterday and in the past. Just stay in zone, stay in attack mode. Just lost them today.”

Henry attacked Sosa with fastballs to jump ahead 0-2. Phillies fans quieted as Henry prepared to throw his final pitch. Sosa didn’t make hard contact — the ball was hit at 90.6 mph. But it found grass in center field.

In the 10th, Realmuto singled to put runners on the corners with no one out. Henry wanted to throw Crawford a cutter in. The hope was to get a quick lineout or weak contact.

Instead, the cutter caught too much of the plate. The Nationals retreated to the dugout and the clubhouse, imagining what could’ve been.

“They’re pretty upset right now, which you like to see,” Butera said. “These guys are competitive. They want to win. You hear how quiet it is in the clubhouse right now. There’s some guys pretty upset walking out of the dugout. ... These last two games have been pretty frustrating. We thought we had all three this series.”