The Washington Nationals’ clubhouse filled slowly Monday afternoon, same as usual, but something was different. Something subtle. Something noticeable only because so little ­changes in the months-long slog of a baseball season.

Players came home from their final road trip of the regular season to find someone had lined the circumference of their large, oval clubhouse with plastic. The person had rolled up sections above lockers and tied them with twine. With eight games left at that point, the Nationals could be just days away from spraying all manner of bubbly ­beverages.

The Nationals weren’t there quite yet, but they later inched closer with a 7-2 drubbing of the Philadelphia Phillies in the opener of a five-game series. They shaved their magic number to clinch a spot in the postseason to three and reclaimed sole possession of the National League wild-card lead with a half-game edge over the idle Milwaukee Brewers. The Chicago Cubs, who had the night off as well, sank to 4½ back of the Nationals. Seemingly the only question left is whether the one-game playoff will be in Milwaukee or Washington.

The Nationals didn’t seem pleased with the reminders of their postseason positioning. Starter Patrick Corbin and Manager Dave Martinez shrugged off the plastic, but it frustrated Adam Eaton. The right fielder said he discussed the decision with someone and “it won’t happen again.” He joked he wanted to “do a Chris Sale and rip every single one of them down,” referencing his former teammate on the Chicago White Sox who once infamously cut up jerseys in the clubhouse before a game because he didn’t want to pitch in them.

“I’m not happy with that,” Eaton said. “It’s a distraction in my book, and [it] shouldn’t have happened.”

The Nationals won with offense, which they hadn’t done much during their struggles of the past three weeks. They homered three times in the first three innings — Eaton to right in the first, Yan Gomes to center in the second and Trea Turner to left in the third. Eaton’s career-high 15th homer fulfilled a Nationals fan’s pick for “Dinger of the Day” in a stadium promotion. The choice of the 30-year-old outfielder impressed the team.

“I want that fan,” Martinez said, laughing. “That's pretty impressive. That’s the first thing we all said [in the dugout], ‘Get that guy down here!’ ”

Anthony Rendon and Asdrúbal ­Cabrera drove in runs in the fifth to push the lead to 5-0 on a night when Corbin was dealing. The left-hander allowed one run over six innings, and he showcased usual dominance with his slider while flashing a new development with his fastball. The game plan called for some up in the zone at times because the Phillies have laid off his slider in the past, and Corbin threw some Monday “kind of short,” Martinez said.

Corbin got Bryce Harper to swing through a 94-mph heater in the third inning for a strikeout, and he fanned Rhys Hoskins with the same approach in the fourth. The swing-and-miss stuff up in the zone is a promising development should the Nationals follow through on what they’ve discussed for the past month and use Corbin as a matchup lefty out of the bullpen in the postseason.

“My fastball felt really good today,” Corbin said. “I thought I was able to locate it. . . . Kind of kept them off balance. Didn’t want to leave any breaking balls there for them to do some damage.”

The bullpen secured nine outs with Fernando Rodney in the seventh, Daniel Hudson in the eighth and Javy Guerra in the ninth. The Nationals warmed Sean Doolittle for the final frame before Phillies reliever Edubray Ramos walked in a pair of runs in the eighth.

The plan for Doolittle instead of Hudson for the ninth was still notable — not long ago, a four-run lead in the ninth would still have been a situation for Hudson. Doolittle still hasn’t had a save opportunity since his return from the injured list at the beginning of this month.

This team is still dealing with the implications of its poor play to start September — which included losing 10 of 16 and squandering the cushion it built all summer — but for one night at least, it didn’t need to worry about its closer at all.

Doolittle’s readiness to resume closing duties would be the latest development indicating the team’s resurgence. Players and coaches expressed relief that, after spending the past three weeks almost exclusively on the road, they had finally returned home for the season’s final week. Martinez, who had a medical scare early last week, received positive results on a scheduled, follow-up doctor’s visit. He walked out of the clubhouse before the game, flashed a double thumbs-up and chirped, “Clean bill!”

No one embodied this team’s past six weeks better than Eaton. The right fielder was scorching in August and then hurt his knee. He returned hobbled and has slumped through much of September.

But Monday, he mashed a 444-foot homer into the second deck in the first inning, singled in the third, legged out a bunt hit in the fifth and walked in the eighth.

“I am in the best shape in September I’ve been in my entire career, by far,” he said. “Just being able to run, I feel very strong.”

Eaton was back, and so was his team. The Nationals jogged off the field Monday night one day closer to unfurling the plastic in the clubhouse.