NEW YORK -- An early September series last season between the New York Mets and Washington Nationals laid the groundwork for the Mets' trip to the World Series while spelling the end of the Nationals' playoff hopes.

Washington hopes to return the favor this weekend.

The National League East-leading Nationals head to New York on Friday for the opener of a three-game series at Citi Field. Washington, which was off Thursday, enters on a three-game winning streak following a sweep of the Philadelphia Phillies this week. The Mets had their three-game winning streak snapped in a 6-4 loss to the Miami Marlins on Thursday night.

Unlike a year ago, the NL East is not up for grabs as September begins. Last season, New York entered a three-game series that began on Labor Day with a four-game lead but swept Washington and never trailed by fewer than six games the rest of the way.

Now, the Nationals (78-55) lead the second-place Mets (69-65) by 9 1/2 games and are already playing with October in mind. The Nationals/Montreal Expos franchise has not won a playoff series since 1981, the longest drought in the "big four" sports.

"I think we're starting to jell a little bit," Nationals left fielder Jayson Werth said Wednesday following Washington's 2-1 win over the Phillies. "Once we get into about halfway through September, I hope we're hitting on all cylinders and we can carry that through as long as we can."

While a second consecutive division title appears out of reach, the Mets also enter the weekend with hopes of reaching the postseason. New York won nine of its past 12 games to move within two games of the St. Louis Cardinals in the race for the NL's second wild card.

If the Mets are to return to the playoffs, they will have to do so with a piecemeal roster. Five of the 10 players who took the field against the Kansas City Royals on Opening Day are out for the season, including second baseman Neil Walker, who confirmed Thursday he soon will undergo surgery to repair a herniated disk in his back.

In addition, shortstop Asdrubal Cabrera (left knee) and left fielder Yoenis Cespedes (right quad) were each on the disabled list in August are likely going to need semi-regular days off down the stretch. Neither player started Thursday, though Cabrera hit a two-run, pinch-hit home run in the ninth, an inning after Cespedes struck out as a pinch hitter.

"It's a tough situation -- that's exactly what it is," Mets manager Terry Collins said. "That's part of the gig, and that's why we've got backup players here."

Mets right-hander Noah Syndergaard (12-7, 2.55 ERA) is scheduled to take the mound Friday against Nationals right-hander A.J. Cole (0-1, 4.97 ERA).

Syndergaard, who ranks third in the NL in ERA, has allowed a total of three earned runs while winning each of his past three starts. In three starts against the Nationals this year, he is 1-2 with a 4.91 ERA. He has a 2-2 record and a 3.12 ERA in six career starts vs. Washington.

Cole, who will be making his third start of the season and his fourth as a major-leaguer, has never faced the Mets. In his most recent outing, he gave up three runs in 5 2/3 innings during a no-decision against the Colorado Rockies on Saturday.