With 13 games to go in the regular season, the Mets (84-65) hold a shrunken, but still sturdy, six-game lead over the Washington Nationals in the National League East. That would seem safe enough, except for one small problem: The Mets’ lead is, in some respects, just three games, not six.

And that’s because the Nationals (78-71), who also have 13 games to go, play the last three of those at Citi Field, on the first weekend in October. From their point of view, they do not have to wipe out the Mets’ six-game lead by the time they arrive in Flushing. To stay alive in the N.L. East race, they just have to cut the lead in half and then take their chances that they could then sweep the Mets and force a one-game playoff.

True, this is not the most realistic scenario in the world but for sure it’s probably enough to keep the Nationals motivated, and the Mets a little nervous, as both teams play out their remaining games.

Neither team, it should be noted, has a particularly difficult schedule over the final leg of the season. The Nationals, who are playing better of late after underachieving with a talented roster for much of 2015, have seven games at home over the next week — against Baltimore, Philadelphia and Cincinnati — before heading to Atlanta and then their potentially fateful encounter with the Mets. Except for the Mets, all of those teams are under .500.