Sean Doolittle understood the importance of the series. It might have been early in the season, it might have been only three games, but the Washington Nationals closer believed his up-and-down team needed to take advantage of its crack at the then-MLB-worst Miami Marlins, a team he politely described as “not playing their best right now.” When Doolittle called the road trip “really important,” he meant the Nationals needed to establish consistency and beat the struggling opponents they should. But in a small way, the Miami series represented something bigger.

With four teams expected to vie for the National League East crown in what could be an unusually crowded race, it’s the fifth team that could decide the division.

Entering Monday, Baseball Prospectus projected the Nationals to finish third in the NL East with 83.9 wins, behind the Philadelphia Phillies (86.7) and New York Mets (85.6) and slightly ahead of the Atlanta Braves (83.2). The major leagues haven’t had four teams finish within four games of one another in a division since the 1980s, when twice the top five squads in the seven-team American League East ended up within 3.5 games. No matter how much stock you put in advanced analytics, this race should be close.

That’s why the focus returns to Miami. The Marlins are predicted to win 65.4 games, and where those victories come from will be crucial. As Philadelphia, New York, Washington and Atlanta jockey for position, as the margin for error against one another shrinks down the stretch, which of the four can avoid beating themselves and rack up the most wins against the Marlins could become a critical edge in a division likely to be decided by a game or two.

Consider the numbers because, as it turns out, they mostly support the old coach’s axiom of “Beat the teams you’re supposed to beat.” Since 2001, when MLB instituted its unbalanced schedule for teams to play each divisional opponent 18 or 19 times, there have been 11 races that resemble what this year’s NL East is projected to look like. In each, two to three teams finished within four games at the top of the division while a bottom-feeder drifted into last place by double digits.

Every time, the contenders’ record against the cellar-dweller was important. Almost always, the contenders were no more than four games above or below .500 against the division’s other teams. Altogether, the contenders averaged a .501 winning percentage against them, so while most of the division’s teams bludgeoned one another to a near-draw, games against the cellar-dwellers became chances to get ahead.

In those 11 races, the contender with the best record against the last-place squad won the division seven times.

The difference between division winners and runners-up was small, even against cellar-dwellers. Overall, the winners finished 13-6 against the last-place team while the runners-up averaged a 12-7 record against them. Last season, the Milwaukee Brewers illustrated the point when they tied the Chicago Cubs for the NL Central title because they took advantage of the last-place team. The Brewers beat the Cincinnati Reds, the division’s worst team, 13 times in 19 games, while the Cubs took just 11 from the Reds. In the one-game tiebreaker for the division, the Brewers then beat the only team that still mattered.

If this trend holds true this season, the Nationals are already behind. Atlanta, New York and Philadelphia are a combined 7-2 against Miami while, over the weekend, Washington went 1-2, becoming the first team in the majors to lose a series to the Marlins.

In the first game Friday in Miami, the Nationals unraveled in a decisive sixth inning to lose, 3-2. They fell again Saturday when the then-worst run-scoring offense in the big leagues knocked around ace Max Scherzer for 11 hits and six earned runs. Washington’s No. 2 pitcher, Stephen Strasburg, stopped the potential sweep with 11 strikeouts over eight scoreless innings for a win Sunday.

For his part, Ryan Zimmerman rejected the supposed importance of one early series because “it’s April” and “every win is important.”

“It doesn’t matter who you are playing,” the Nationals first baseman said. “Everyone says this team over here [the Marlins] is going to lose this many games and all that, but they are a big league baseball team with some talented young kids. We have to go out there and play good baseball and beat you. So I hate when people say that about big league teams.”

The Nationals’ start against the Marlins is, of course, not insurmountable. There’s a long season ahead. But, when every game matters, the Nationals are already playing from behind.