PHILADELPHIA -- Chasing their first home series win over division-rival Washington in nearly two years, the Philadelphia Phillies were just one out away from making it happen before the Nationals' Ryan Zimmerman made the 35,000-plus fans at Citizens Bank Park wait just a little longer.

Though not too much longer.

After watching a three-run lead disappear on one Zimmerman swing in the top of the ninth, the Phillies recovered to beat the Nationals 4-3 on a walk-off single by second baseman Cesar Hernandez just a half-inning later.

The Phillies hadn't won a series against the Nationals at Citizens Bank Park since taking two of three between April 10-12, 2015.

A two-out single in the bottom of the ninth by Hernandez (2-for-5, two RBIs), scored pinch hitter Daniel Nava, who had walked to lead off the inning and advanced on a Freddy Galvis single.

"To win two out of three from one of the better teams in the NL was special," Phillies manager Pete Mackanin said. "Cesar put the ball in play like we preach. A broken-bat single to win the game."

Zimmerman's three-run home run off Jeanmar Gomez with two outs in the ninth inning kept the Nationals (3-3) alive in a game the Phillies had controlled almost the entire way up to that point.

Phillies starter Jeremy Hellickson (1-0) was cruising through the first five innings, throwing 70 pitches and holding Washington scoreless with just a solitary hit. But he departed before the top of the sixth inning with what the Phillies called a "right forearm cramp," leaving it up to the bullpen to get the job done.

"That was weird," said Hellickson, who attributed the cramping to dehydration. "First time it happened in a game. My hand curled up. It's frustrating. I felt like I could go seven, eight innings."

Relievers Joaquin Benoit, Pat Neshek and Hector Neris kept the Nationals' offense quiet through the eighth inning before Gomez blew it in the ninth.

The embattled closer gave up a one-out single to Adam Lind and then walked Jayson Werth and retired Stephen Drew on strikes before Zimmermann came in to pinch hit. The 13-year veteran took a 2-0 sinker and smashed it over the wall in left field, scoring his two teammates as boos rained down upon Gomez.

It's been a struggle for the Phillies' closer ever since last September, which he entered with a 2.97 ERA but gave up 17 runs in eight innings. In his 2017 season debut, Gomez gave up two runs against Cincinnati but managed to hold onto the save in a 4-3 win.

After Sunday's blown save, it's hard to see him staying in the role much longer.

"We'll see," Mackanin said. "We're gonna discuss what we have to do what's best for the team. I'm considering it."

Galvis (2-for-4, RBI) opened up the scoring for Philadelphia in the second inning with an RBI single, scoring first baseman Tommy Joseph after Washington starter Stephen Strasburg walked two batters earlier in the frame.

The Phillies (3-3) got to Strasburg twice more in the fifth inning. Three batters after catcher Andrew Knapp started off the inning with a double for his first career hit and then moved to third on a sac fly, Hernandez brought him home with an infield single.

Hernandez scored one batter later on a double by left fielder Howie Kendrick, who went 1-for-3 with his fifth RBI of the year.

"All their runs were scored today with two outs, and that's what's been eluding us, is a two-out hit," Nationals manager Dusty Baker said. "It seems like other teams have been getting them early in the year, and they're certainly not any better hitters than we are, we just have to keep grinding and the wins will come."

Zimmerman's home run saved Strasburg (1-0, 3.21 ERA) from taking the first loss of his career at Citizens Bank Park. In his previous six starts in Philly, he'd been 2-0 with a 1.22 ERA, having never given up more than two runs in any of those outings.

The two-time All-Star and 15-game winner a year ago certainly wasn't at his best this time around. The Phillies tagged him for the three runs -- all earned -- on five hits in seven innings, while drawing three walks against eight strikeouts.

"I made some good pitches early, they just didn't call them," Strasburg said. "Just have to keep chipping away and that's all I can do."

NOTES: The Nationals designated RHP Jeremy Guthrie for assignment after the 38-year-old gave up six hits and 10 runs in two-thirds of an inning in a 17-2 loss on Saturday. To fill his spot, they called up veteran RHP Matt Albers from Triple-A Syracuse. ...Following the game, the Nationals announced they signed free agent RHP Joe Nathan to a minor league contract; Washington released the 42-year-old Nathan in March. ... The Phillies will open a three-game series at home against the New York Mets on Monday. Philadelphia will send RHP Jerad Eickhoff (0-1, 2.70 ERA), will match up against RHP Jacob deGrom (0-0, 0.00 ERA). ... Washington returns home Monday for a three-game series against the Cardinals. The Nationals will throw RHP Tanner Roark (1-0, 3.00 ERA) against St. Louis RHP Adam Wainwright (0-1, 3.60).