Adam LaRoche continues to rake for the Nationals, crushing a three-run home run — his 26th of the season — that earned him a curtain-call in the fifth inning. (Jonathan Newton/The Washington Post)

The playoffs start in over a week. With Ryan Zimmerman’s return this past weekend, the Washington Nationals have been whole again for the first time in two months. Their focus has been on keeping everyone healthy and securing the National League’s top seed in the playoffs. The last thing they need now is an injury, especially to a key player.

And even though the Nationals beat the New York Mets, 4-2, on Tuesday night as Adam LaRoche continued his fine bounce-back season and Tanner Roark delivered another strong start, watching Denard Span walk gingerly off the field in the third inning may have been the most lasting image. After making a spectacular head-first diving catch, Span left the game with a right knee wound that, for now, isn’t considered serious.

“When he starts limping, of course there’s some tense moments in the dugout,” a relieved Manager Matt Williams said.

The Nationals’ win trimmed the magic number to clinch the best record in the NL to two. Should the Los Angeles Dodgers fall to the San Francisco Giants late Tuesday, the Nationals could lock up the NL’s top seed on Wednesday and begin resting more players. The Nationals will already be without Span, who has been one of the team’s best players this season and will sit out Wednesday.

With two outs in the third inning and Roark and Mets starter Bartolo Colon locked in a scoreless tie, left fielder Matt den Dekker hit a slicing ball to center field. The ball tailed toward left-center field and Span circled toward it.

The Post Sports Live crew discusses whether the Nationals would be better off facing the Pittsburgh Pirates or the San Francisco Giants in the first round of the MLB playoffs. (Post Sports Live/The Washington Post)

Span dove and caught the ball at the warning track. He landed on his bent right knee, spun over and hit the padded wall. Roark stood on the pitcher’s mound, grinning in disbelief and waited for him at the dugout steps. Span got up and jogged slowly toward the dugout, favoring his right knee, which was scraped badly and bruised.

“When I took about three or four steps trying to jog in, that’s when my knee felt a little funny,” he said.

At this point of the season, Williams has been exercising more caution than normal with players. Any nick or bruise need not be worsened. And with Span, the Nationals’ valuable everyday center fielder, Williams didn’t need to take any risks.

“I wasn’t concerned with him hitting the wall,” Williams said. “The way he went down was concerning. But they’re going to play. You can’t play any differently. You have to go get it. You have to dive. You have to go in and break up two. All of those things. Like the way we’ve been playing all year. We can’t change now.”

Span was replaced in center field and in the bottom half of the inning by rookie Michael A. Taylor. In his second at-bat filling in the fifth inning, Taylor tied the game at 1 when he sliced an RBI double down the right field line off Colon. Meanwhile, Span iced his knee several times.

Span said his knee has full strength and can take his body weight. But if pain persists, the team doctor told Span he would take another look. Span said it was too soon to say if he was worried.

“If a couple of days go by and it doesn’t feel good, then I will be,” he said. “I think being able to walk and put pressure on it, that’s a good sign to me.”

The Nationals took control in the fifth inning when LaRoche crushed a three-run home run off Colon that smacked off the back of the Nationals’ bullpen in right field. Jayson Werth drew a two-out walk ahead of LaRoche that set up the home run. Nationals Park fans applauded and drew LaRoche from the dugout for a curtain call. His 11-year-old son Drake gave him a hug from the tunnel that led to the home clubhouse.

A year after the worst non-injured season of his career, the 34-year-old has maintained his strength, fixed his timing at the plate and has smashed a team-leading 26 home runs and 91 RBI.

“I felt like I was kind of swimming upstream the whole year,” LaRoche said. “This year, [gratifying] to be able to bounce back and contribute more.”

Tuesday was, mostly, a joyous day for the Nationals in front of their home fans. They returned from their longest road trip of the season, a three-city journey in which they went 9-2. They won the NL East title, their second in three seasons, in Atlanta against their heated division rival. They also welcomed the longest-tenured National, Zimmerman, back to the active roster.

Fans cheered louder than normal for Roark as he walked from the bullpen to the dugout before the game and photos of the clinching celebration appeared on the scoreboard. They gave Zimmerman a standing ovation when he pinch-hit in the seventh inning, his first home at-bat in two months. They also gave Roark a standing ovation after departing in the seventh inning with one out and two on and the Nationals ahead 4-1.

Williams played the matchups to complete the seventh inning, trying to counter Mets Manager Terry Collins’s substitutions. Ross Detwiler walked a batter to load the bases and then gave up a sacrifice fly that trimmed the Mets’ deficit to 4-2. With the bases loaded again by Aaron Barrett, Jerry Blevins escaped the inning by getting a popup. Tyler Clippard fired a scoreless eighth inning, pitching around a triple on a ball that was misplayed by Bryce Harper, and Drew Storen needed 25 pitches but secured his 10th save.

The Nationals moved one win closer to their goal of securing the NL’s top seed but, also, hoped that Span’s injury would remain simply a scrape and bruise.

“I have a couple of days or have some time for it to heal up,” he said. “Hopefully, I’ll be praying [Tuesday night, hopefully that things will heal a lot faster].”