Nationals' Denard Span, bottom, is safe at second as Philadelphia’s Chase Utley bobbles the throw to first. (Laurence Kesterson/AP)

The Washington Nationals’ lucky break steamrolled them Sunday afternoon. The Philadelphia Phillies scratched Cole Hamels from his start after he came down with the flu Saturday, which convinced the Nationals the world had done them a favor. Rather than one of baseball’s most accomplished lefties, they would face Roberto Hernandez, a journeyman who lugged a 5.74 ERA to the mound.

In the Nationals’ 1-0 loss at Citizens Bank Park, Hernandez made clear the Nationals had run into something far different than luck. He fired 71 / 3 scoreless innings as the Nationals wasted Gio Gonzalez’s dazzling start, cost themselves another opportunity to overtake the scuffling Atlanta Braves and accepted a series loss in the first meeting with the Phillies.

Once Hernandez exited, the Nationals stranded the tying run on third base in the eighth and succumbed to closer Jonathan Papelbon in the ninth after Zach Walters’s liner to right scared the foul pole. They managed just five hits, all of them singles, two of them off Denard Span’s bat. Gonzalez absorbed the loss even though he allowed one run on four hits in 71 / 3 innings himself.

For the second straight game, the Nationals missed a chance to move into first place. The season’s first month, plus the first few days of May, has settled nothing in the National League East. The Braves still lead despite six consecutive losses, but they are barely holding off all four challengers. While the Braves’ record tumbled to 17-13, every NL East team has a winning record and is within 11 / 2 games of first.

“It’s been ebb-and-flow for the season so far,” Manager Matt Williams said. “With some really good stretches and some not-so-good stretches. Considering what’s happened to us and where we’re at, we’re okay.”

Having finished their road trip 3-2, the Nationals remain in the mix despite a confluence of injuries. Doug Fister, Wilson Ramos, Ryan Zimmerman, Bryce Harper and Scott Hairston have all missed time on the disabled list. Now, Fister is scheduled to start Friday, Hairston should return Monday and Ramos hit a homer Sunday afternoon in Hagerstown.

“For us to be where we are right now with all those injuries, I say it’s even better,” utility man Kevin Frandsen said. “When those guys start coming back, it’s almost like a trade deadline for all of us. We’re going to get more and more shots in the arm. We can’t be looking forward to that, but we can control what we’re doing right now and keep us in a position to stay in it. And when those guys come in, hopefully we take off.”

With the Nationals down to their last out Sunday afternoon, Sandy Leon strode to the plate and Walters stood on deck. They had started the season in the minors. Injuries had turned them into reinforcements. A diminished lineup stifled by an emergency starter had turned them into last resorts.

Still, they clawed. Leon ripped a single to right. The wind gusted out toward right field, nearly ripping pennants off flag poles. A switch hitter who had smashed three homers in 16 plate appearances, Walters batted from the left side.

Walters drilled one pop fly that the wind pushed foul, short of the fence. Two pitches later, Walters crushed a line drive down the line that hooked to the right of the pole. Having watched Walters pull two near-misses, Papelbon fired a sinker outside, and Walters chased to finish an at-bat that, after nearly changing the game, ended it.

“He had one heck of an at-bat there, giving himself two chances,” Frandsen said. “You really can’t ask for anything better than that. He battled. I wouldn’t say he battled. I thought he owned that at-bat.”

Gonzalez was great but not immune to the Nationals’ first-inning struggles. Jimmy Rollins hammered a high fastball to the left-center field gap for a triple, and Chase Utley scored him with a single up the middle. Gonzalez stopped the damage, but the Nationals have allowed 32 runs in 31 first innings this year.

The Post Sports Live crew debates whether Bryce Harper's intense style of play attributed to his hand injury. (Post Sports Live/The Washington Post)

The Nationals’ best shot at Hernandez came in the first. Frandsen drew a one-out walk. Jayson Werth followed with a smash to third base, and the ball deflected off Jayson Nix and trickled into shallow left.

Frandsen’s hell-bent base running has sparked the Nationals, and he tried another bold play by bolting for third. John Mayberry Jr. scooped the ball with his bare hand, and his throw beat Frandsen’s headfirst dive.

In the dugout afterward, first baseman Adam LaRoche told him, “Take that chance every time.” With one out, Frandsen reasoned, the benefit of reaching third base — where he could score on a sacrifice fly — far exceeded the risk. Frandsen also knew Werth would be aggressive behind him, and so the Nationals would have at least one runner in scoring position.

“Guys doing that has won us some ballgames,” LaRoche said. “And it’s going to win us a lot more.”

Once Hernandez escaped the first, he dominated. The Nationals either pounded his heavy sinkers into the ground or lined them into gloves. At one point, Hernandez retired 15 of 17 Nationals, including 10 straight.

“He just had that sinker going, and he kept it down,” LaRoche said. “I’m sure we chased some pitches on top of that.”

As Hernandez cruised, Gonzalez matched him. He allowed only two more hits after the two he yielded in the first inning. He struck out seven, walked two and retired 15 of the final 17 batters he faced, lowering his ERA to 2.91.

“It was just one of those games,” Gonzalez said. “You’ve got to keep your team in it as long as possible.”

The Nationals’ chance in the eighth fizzled. Span led off the inning with a single. Even after the count ran to 2-0 in Frandsen’s favor, Williams kept the bunt on. Frandsen dropped a sacrifice and pushed Span, the tying run, to second. Phillies Manager Ryne Sandberg pulled Hernandez and called on Mike Adams.

Adams induced a groundout from Werth, which left the inning to LaRoche. Sandberg summoned left-hander Antonio Bastardo, who promptly walked LaRoche.

Sandberg’s maneuvering had led to a nightmare matchup for the Phillies. No other reliever was ready to face Anthony Rendon, who walked to the plate hitting .481 against left-handed pitchers this season. Still, Rendon watched strike three, a sinker that catcher Carlos Ruiz may have yanked over the plate from outside the corner. The tying run withered 90 feet away.

“I thought it was a ball,” Rendon said. “It’s not what I think. It’s what the umpire thinks.”