Pirates catcher Jacob Stallings, center, celebrates with teammates after hitting a walk-off bases loaded single off Washington Nationals relief pitcher Yusmeiro Petit in the 11th Friday night at PNC Park.

PITTSBURGH — Rookie Jacob Stallings’ pinch-hit single in the 11th inning lifted the Pittsburgh Pirates over Washington 6-5 on Friday night, preventing the Nationals from clinching a postseason berth.

Pittsburgh loaded the bases with one out against Yusmiero Petit (3-5) when Francisco Cervelli doubled, Andrew McCutchen was intentionally walked and Pedro Florimon walked. Sean Rodriguez struck out and Stalling, a son of University of Pittsburgh men’s basketball coach Kevin Stallings, grounded a 3-2 pitch into left field.

Pittsburgh’s seventh win in nine games kept the Pirates on the fringe of the NL wild-card race.

Washington lost for the fifth time in six games. The Nationals have magic numbers of one for a playoff berth and two for an NL East title.

Rodriguez’s two-out RBI double in the ninth inning tied the score 5-5.

Mark Melancon blew a save for the first time in 13 chances since he was acquired from Pittsburgh on July 30.

Wilson Ramos and Danny Espinosa homered for the Nationals. Bryce Harper had three hits and Ryan Zimmerman hit a pair of doubles.

Zimmerman’s RBI double in the second inning opened the scoring and was the 1,500th hit of his 12-year big league career. Espinosa followed with 23rd homer for a 3-0 lead.

Ramos led off a two-run sixth with his 22nd homer, a drive off Antonio Bastardo. Jayson Werth drew a bases-loaded walk later in the inning as the Nationals went back ahead 5-3.

Adam Frazier had a sacrifice fly in the bottom of half.

Pirates left fielder Gregory Polanco left the game in the first inning when bruised the left side of his face when crashing into the fence while chasing a double by Harper.