The Nationals head toward the home stretch with a difficult schedule but one they must manage. (John Amis/AP)

It wasn’t supposed to be like this. The Washington Nationals weren’t supposed to virtually concede the National League East crown with three weeks to play. They weren’t supposed to, in the first week of September, play as poorly as they have since late May, with the stakes now as high as they have been since the early spring.

Yet they did. The Nationals began last week still pushing for a serious chance at the division title. Win or sweep their three-game series against the New York Mets and at least split with — or even take three of four games from — the Atlanta Braves, and the Nats could have been as close as 3½ games out of first, with three head-to-head matchups left with the division-leading Braves. The week was a missed opportunity. The Nationals won once against the Braves to avoid a sweep and once against the Mets after a historic, seven-run comeback in the bottom of the ninth. Catcher Yan Gomes, though, pumped the brakes on the postseason implications of the 2-5 stretch.

“I don’t think we need to get too far ahead of ourselves. I think we put ourselves in a good position,” he said after Sunday’s 9-4 win in Atlanta. “We came in here and wanted to gain ground on them. It didn’t happen. We have to move on.”

The Nationals entered Monday’s games with a 0.3 percent chance of winning the NL East, according to FanGraphs — about the same chance the site Vegas Insider gave the Washington Redskins to win the Super Bowl this season (0.33 percent). The Nationals’ likeliest path to the postseason with 20 games left is the wild card, a tight race that seems poised to constrict further in coming days. Five teams entered Monday within seven games of the Nationals, who start this stretch atop the wild-card standings.

The Chicago Cubs occupied the second wild-card position, three games behind the Nationals, and they were followed by the Arizona Diamondbacks (1½ games further back), Milwaukee Brewers and Philadelphia Phillies (two) and Mets (four).

Most worrisome for the Nationals is that, with the division title out of the picture, they will be reframed as the leader, not the chaser, of this playoff race. They now must maintain their grip on the top wild-card spot with the second-hardest remaining schedule among playoff competitors, according to weighted opponent winning percentage, which factors in how many games are played against each team. The slate starts Tuesday: three games in Minnesota against the American League Central-leading Twins, three at home against Atlanta and three in St. Louis against the Cardinals. Then there is a day off and a three-game set in Miami against the last-place Marlins before an eight-game homestand to end the season: five with the Phillies and three with the Cleveland Indians.

This is concerning because the Nationals have, at times this season, struggled against teams above .500. Each of those closing opponents, save the Marlins, has a winning record. The Nationals need to play their best against the best competition if they want to maintain home-field advantage for a potential one-game wild-card playoff. Playing at home hasn’t been a boon for NL teams since the single-elimination wild-card round started in 2012 — road teams are 5-2 in that game — but the Nationals would prefer to open the postseason at Nationals Park rather than somewhere else, such as Wrigley Field.

The most clear and direct threat to the Nationals is the Cubs. It seems unlikely Chicago will catch the Cardinals for the NL Central title — St. Louis owned a 4½-game lead entering Monday — but it’s possible. The Cubs had the second-easiest remaining schedule among those still in the playoff hunt, according to weighted opponent winning percentage, and seven head-to-head matchups left with the Cardinals, including a three-game series in St. Louis on the last weekend of the season. The one comfort for the Nationals is that neither the Cubs nor the Cardinals have an ace the caliber of Max Scherzer or Stephen Strasburg.

The Diamondbacks used to have one in right-hander Zack Greinke, but they dealt him to the Houston Astros at the trade deadline, seemingly sinking their season. Yet Arizona hosted Washington two days later, won two of three against the Nationals and hasn’t slowed since. The Diamondbacks have relied on young pitching and do-everything position player Ketel Marte and now have a chance to get into the tournament. Their remaining schedule was the third weakest entering Monday, with 12 of their final 19 games at home. The only slate easier by winning percentage was that of the Brewers, who had nearly the opposite home-road split.

The Phillies and Mets are also on the outside but still very much players in the postseason chase. The Phillies might not contend for much longer — they have a hellacious 10-day, 11-game road trip against three of baseball’s top eight teams in the middle of the month — but they will still be a large factor for the Nationals. The last five games of that road swing come at Nationals Park.

The Mets, despite having one of the only rotations in baseball that could keep pace with the Nationals', had lost 10 of 15 entering Monday and sit one bad series away from spending the rest of the season playing spoiler. You could argue the Nationals’ historic comeback, so deflating that Mets center fielder Brandon Nimmo told reporters it was “hard to do even in a Little League game,” dealt the biggest blow to their season. They have a mediocre remaining schedule, but with 14 of their last 20 games at Citi Field, they have the most advantageous home-road split of any team in contention. Whether the Mets will remain in the race will start to be determined this week with four home games against the Diamondbacks.

The Nationals, for now, can only put their heads down and try to play their way out of this predicament. They know, as several outrageous games in the past few months have shown, that anything can happen in one game, such as a wild-card elimination matchup. But they have three weeks left to put themselves in the best position to win it.

“It’s September. You got to win every day,” Scherzer said. “That’s just how it is. You’ve got to win every day.”

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