After a sweep by the Mets, the Nationals head into August struggling to maintain their early season momentum. Are the World Series favorites still likely to win the division? (Post Sports Live/The Washington Post)

The rest of the Washington Nationals’ season — and their chances of fulfilling much or all of their preseason promise — is as easy as 1-2-3. Or, rather, three different 1-2-3s.

• First, Jayson Werth, Ryan Zimmerman and Anthony Rendon must hit. If they return close to career norms, with Bryce Harper in their midst, they are as potent a mid-order as exists in baseball.

Rendon homered to center, singled to left and doubled to right off the Mets’ Noah Syndergaard on Saturday. On Tuesday, he ripped four line drives off three different pitchers. Consider him “back.” Werth and Zim we’ll discuss later.

• Second, Casey Janssen, with a 1.40 ERA in his last 20 games, Drew Storen with a 1.30 ERA the last two years and Jonathan Papelbon, with a crazy-good 2.32 career ERA, must form a 1-2-3, back-of-bullpen trio that’s comparable to any in baseball — except the Royals. All have been quality closers. All say they are healthy and pitching at the high level they expect.

If Matt Williams had used them as the baseball gods intended Saturday — to get the last nine outs with a 2-1 lead after a rookie gave him six strong innings, the Nats might still be in first place (tied with the Mets).

While fan favorite Drew Storen has struggled closing playoff games, Jonathan Papelbon has proven himself to be more consistent. Who's more suited to pitch the ninth inning of a playoff game? (Post Sports Live/The Washington Post)

• Third, Williams must get playing time for Danny Espinosa, Clint Robinson and Michael A. Taylor to keep that 1-2-3 productive. They’ve earned it and are a big part of the future, with 13 seasons (combined) of team control. Use ’em and have a top bench; let ’em rust, play a pat lineup and you’ll lose their punch. Come October, when depth wins late and close games, they won’t be special.

Williams, who struggled with building a capable bullpen this year even though he had a fine closer in Storen, must now do an even tougher juggling act. What he couldn’t do for months with Tyler Clippard gone, Craig Stammen out for the season, Blake Treinen a disappointment and no young lefty panning out, he will need to accomplish now in managing a deep bench. That will require “rotating” players with entrenched star status once or twice a week, even if healthy. Touchy.

Managing is tougher than simply writing the same eight names on a lineup card every day and using your backup catcher once a week. “It’s a thankless job,” Werth said. “Can you keep us [starters] fresh, handle personalities and still have the knack for piecing together [effective] lineups? It seems like either you do or you don’t. It’s not easy.”

On Tuesday, Williams said he welcomed that task and specifically mentioned “really nice years” by Espinosa and Robinson. Taylor will still play every day until Denard Span gets back later this month.

Nonetheless, players who have been as outstanding as Ian Desmond, Zimmerman, Span and Werth usually don’t like to sit — ever — if they’re healthy. Invaluable Yunel Escobar, on the edge of the batting-title race, might not like it either. What’s good for the team can feel like “benched.” In light of the Nats’ squandered 2013 season and their 55-50 record now, it’s time for egos and “walk years” to be locked in a broom closet. When in doubt, act like Storen.

Though the Mets’ sweep of the Nats last weekend shows that an interesting NL East race will be with us for a while, “big events” at this point in a season seldom have lasting impact. Of the last 15 World Series champions, eight were not in first place at the two-thirds mark of the season (108 games) and two were in first by one game or fewer.

The Nationals' acquisition of pitcher Jonathan Papelbon pushed Drew Storen out of the closer role, but will it disrupt the clubhouse chemistry? (Post Sports Live/The Washington Post)

The easiest 1-2-3 is the bullpen trio. “I’m throwing the ball like I should and like I know how,” said Janssen, the $5 million free agent whose last five years (2.76 ERA, 83 saves) duplicate Clippard’s six fine Nats years (2.65, 34 saves) but at half the salary and with the addition of Escobar in trade.

Storen is pitching with vengeance. In four games since the Pap trade, he has thrown three balls (total) and retired 12 straight. All he might have lacked was Closer Ornery. Check that box.

The Nats can hardly believe they got Papelbon. Fans think he looks obnoxious. Well, 11 seasons of hitters know he’s obnoxious — to hit. That’s what matters. Werth and Janssen both summarized Papelbon, admiringly, with one word. Can’t use it in the paper. “I just saw when . . . he was pitching: career [2.32] ERA? I mean, it’s ridiculous,” Janssen said.

The hardest and most pivotal 1-2-3 is the power-plus-on-base percentage trio that’s just come off the DL. Let’s assume that Rendon’s 76 missed games do not make him the next fragile Freddie Lynn.

But Werth, 35, has missed 199 games the last four years. All “trauma injuries,” he says, not age. “I’m going to play until I’m 45 — watch,” he says. “My swing has never been better.” He thinks he’s close to going on one of his late-season tears. His double keyed a Tuesday win. But he’s also hitting .205.

Zimmerman has missed 141 games the past two years and hit only .244 when he did play. In the last week, off the disabled list, he has hit two of his longer homers. But he has the kind of heel injury that, every time it gets aggravated, robs power. Right now, he’s running like he’s 27 again. How do you prolong that health? Maybe by using Robinson at first against a tough righty or two each week.

Since the day he arrived, Werth has been the clubhouse voice at pivotal or crisis moments. That’s why he seldom holds court. On Tuesday, after his key double, he was the first — and only — Nat available to be interviewed. Translation: state of the club address from Oldest Member to follow.

“It’s a matter of time, really. We’re a great second-half team. We’ve [had] half our team hurt all year. That’s the reality of it,” Werth said. “When we all get back we’re right there, in first place. We’re a game out now. But I think going forward we can all get back healthy and get rolling, and it’s our division to lose.”

Sounds as easy as 1-2-3. But it’s not. It’s more like 1-2-3, plus 1-2-3, plus 1-2-3. That’s a little harder.

For more by Thomas Boswell, visit washingtonpost.com/boswell.