Stephen Strasburg looks to continue his outstanding run at home and hand the Phillies their 11th straight road loss in the series finale Sunday night.
Jayson Werth had three hits, including his 17th home run, as the Nationals (56-60) rallied from an early 4-0 deficit for an 8-5 victory that extended Philadelphia's worst road losing streak since a 12-game skid from Aug. 28-Sept. 14, 1999.
Darin Ruf and Domonic Brown homered for the Phillies (52-64), who have averaged 2.1 runs while batting .199 during their slide. Michael Young (4 for 32), Kevin Frandsen (3 for 19) and Carlos Ruiz (4 for 24) are among those scuffling on the road.
"When you start losing and you find different ways to lose every night it becomes tough,'' said manager Charlie Manuel, whose next win will be his 1,000th. "You've got to fight through it.''
It doesn't figure to get any easier against Strasburg (5-9, 3.01 ERA), who hopes to lead Washington to its first sweep since taking three straight from San Diego from July 5-7.
The right-hander has pitched particularly well at Nationals Park with a 1.76 ERA in 12 starts, though he's been given an average of 2.5 runs of support while going 4-4 there.
This time, the Nationals are swinging the bats with some confidence. They're 10 for 21 with 14 RBIs with runners in scoring position in this series following a stretch in which they went 7 for 56 with 10 RBIs in those situations while dropping six of eight.
Werth, a former Phillies star, has certainly been on a tear, going 21 for 42 (.500) over his last 14 games.
"He's absolutely raking right now,'' said teammate Bryce Harper. "I'm just trying to touch his bat so I can get some hits in there.''
Strasburg is 1-1 with a 4.43 ERA in four career starts versus the Phillies, but had a dominant performance the last time he faced them in the nation's capital. He struck out nine while yielding one run and five hits over eight innings in a 6-1 win May 26.
Jimmy Rollins homered off Strasburg in Washington last season for his only hit in 12 career at-bats in this matchup. Ruiz has had the most success with a homer and a double in four at-bats.
The Phillies hope to avoid their 17th loss in 20 games overall behind Kyle Kendrick (10-8, 4.36), who has been struggling with a 3-4 record and 6.93 ERA over his last seven starts.
The right-hander allowed five runs over six innings Tuesday, though he retired 10 of the final 11 batters he faced and Philadelphia rallied to beat the Cubs 9-8.
Kendrick limited the Nationals to two runs over 14 2-3 innings in a pair of home starts, but was tagged for five runs and eight hits over five innings in a 5-2 loss at Washington on May 24.
Ian Desmond is 1 for 8 against Kendrick this season, but he's 7 for 15 in his last four games against the Phillies.
Harper has had success when facing Kendrick, going 8 for 17 with three doubles, a triple and a homer.
Philadelphia has not been swept in a series of at least three games by the Nationals-Expos franchise since dropping a four-game set from Aug. 25-28, 2003, while in Montreal.