Nationals 6, Pirates 5 (11): Jayson Werth belted a lead-off double in the 11th inning and scored on Scott Hairston's sacrifice fly after Pittsburgh scored three times to go ahead in the ninth and host Washington extended its winning streak to a season-high six games.Ross Detwiler (2-2) worked two scoreless innings for the Nationals, who moved 6 1/2 games ahead of second-place Atlanta in the National League East. Werth, who entered the game as a pinch hitter in the ninth, began the 11th with a double off Brandon Cumpton (3-4), moved to third on Denard Span's groundout and scored on Hairston's fly ball to left field.Doug Fister allowed two unearned runs over seven innings while Span and Anthony Rendon had two hits apiece for the Nationals, who posted their second straight walk-off victory. Edinson Volquez allowed four runs (one earned) on six hits over 6 1/3 innings for Pittsburgh, which recorded its season-high fifth straight loss and fell 5 1/2 games back of Milwaukee in the NL Central and 1 1/2 behind San Francisco for the final wild card spot.Gregory Polanco snapped an 0-for-19 slump by delivering a two-run double in the ninth off Rafael Soriano to put the Pirates ahead 5-4, but the Nationals answered in the bottom half on Asdrubal Cabrera's RBI single off Mark Melancon. Both starting pitchers cruised through the early innings before Pittsburgh took a 2-0 lead in the sixth after capitalizing on two Washington errors. Jared Hughes replaced Volquez with the bases loaded and one out in the seventh, and the Nationals scored twice when Cabrera's ground ball to first resulted in two Ike Davis throwing errors. The Nationals moved ahead 4-2 on Rendon's sacrifice before Soriano entered in the ninth and allowed the first three batters to reach base safely.GAME NOTEBOOK: Pittsburgh placed RHP Charlie Morton (hip) on the 15-day disabled list and recalled 3B Brent Morel from Triple-A Indianapolis. … Werth was held out of the starting lineup for the seventh time in the last nine games with a sore right shoulder. … Washington improved to 59-7 when scoring four or more runs.