Assuming the playoffs started tomorrow, the Post Sports Live crew debates which Nationals pitcher should start Game 1. (Post Sports Live/The Washington Post)

Doug Fister had rescued the Washington Nationals so often, which made the moment seem so foreign. In the sixth inning Wednesday night, Fister stood stoic on the mound. He had just allowed a go-ahead home run on a hanging curveball and plunked a batter with a stray sinker. Wildness had replaced robotic dominance. Manager Matt Williams walked from the dugout and asked for the ball, perhaps the first time this season someone needed to rescue Fister.

The Nationals swaggered into Citizens Bank Park on Monday as the hottest team in baseball, with 12 wins in 13 games. On Wednesday night, the last-place Philadelphia Phillies staggered Fister and completed a stunning sweep with an 8-4 victory. Fister yielded five runs — his most in any start since his season debut — in 52 / 3 innings on a season-high 10 hits. The Nationals failed to build off their scorching offensive start, but Fister twice lost a two-run lead.

“I let the guys down tonight with some bad pitches,” Fister said. “That’s what it comes down to. I didn’t do my job. A starting pitcher is supposed to set the tone and be the example. From first pitch, I didn’t do that. I’ve got to be better from the start.”

The Nationals had not been swept since June 15, which came against the St. Louis Cardinals. They had not lost three consecutive games since June 27, when Bryce Harper was on the disabled list, Ryan Zimmerman was playing left field and the words “Ice Bucket Challenge” meant nothing.

The Nationals still hold a 61 / 2 -game lead over the Atlanta Braves, who beat the Mets in New York. The sweep in Philadelphia applied pressure to the rest of an arduous road trip. Six games against the Mariners and Dodgers await. They start Friday night in Seattle against Felix Hernandez, perhaps the game’s best right-handed pitcher.

Denard Span returns to the dugout after scoring in the first inning. Span went 3 for 5 and smoked a home run into the upper deck in the fifth inning. (Brian Garfinkel/Getty Images)

“It’s not going to get any easier,” said Denard Span, who went 3 for 4 with a mammoth upper-deck home run. “Philly outplayed us these last three days. Outpitched us, outhit us. That’s why we got to continue to grind.”

The Phillies, whom the Nationals led by 171 / 2 games before they arrived, continued to pester the Nationals, having split their 16 meetings. The Nationals are just 3-6 at Citizens Bank Park. After taking the first two games of the series by a single run, the Phillies used Marlon Byrd’s two-run homer off Ross Detwiler in the seventh inning to create a wider margin of victory Wednesday.

“We lost three in a row, but we played good baseball when we were here,” shortstop Ian Desmond said. “We scored a couple runs against Cole Hamels in a clutch situation. We came out tonight, scored some runs, got the lead. We’re still playing good baseball. We just happened to lose a couple games.”

From May 14 through Aug. 17, the Nationals won 14 of Fister’s 17 starts, and Fister tip-toed into the Cy Young discussion. In his past two outings, both losses, Fister has allowed nine runs, eight earned, over 112 / 3 innings. The starts came after Fister underwent a procedure to remove skin cancer from the left side of his neck, but, “I don’t think there’s any effect there at all,” Williams said. “He missed no time.”

Fister (12-5) pointed to a simple culprit — he has not been locating pitches down in the strike zone. When he leaves balls up, Fister makes adjustments to the rhythm and timing of his delivery. “’I didn’t get them done tonight,” Fister said.

Fister yielded two home runs and struck out only three Wednesday. He stumbled in the first inning after the Nationals gave him a two-run lead, then danced around singles for four innings. Fister carried a 4-2 lead into the sixth.

Byrd led off by flaring a single into center field. Domonic Brown pounded a double to right, which sliced the lead to 4-3. Brown offered Fister a reprieve, running on a grounder to Desmond, who threw him out at third. Fister induced a pop-up from Cody Asche, and he needed only one more out to escape.

Fister moved ahead of pinch hitter Grady Sizemore with two called strikes on offspeed pitches. Fister pitches off feel and how hitters react to him, and he believed he had Sizemore set up to swing over a curveball in the dirt. But Fister elevated the curved, and Sizemore hooked it over the right field fence. The Phillies surged ahead, 5-4.

“I got away from my plan,” Fister said. “I tried to get a little tricky with a couple curveballs. I hung the second one. He’s a great hitter and he’s done it for a while, and you pay for it.”

Fister’s night ended when he misfired a sinker that drilled Ben Revere on the right elbow. Home plate umpire Dan Iassonga issued warnings to both benches. (“There wouldn’t be any reason he would hit Ben there,” Williams said.) Williams trudged to the center of the diamond and took the ball.

“You really can’t say too much,” Span said. “He’s been unbelievable. When he has a game like this, it almost seems like he didn’t pitch good. But he still pitched great.”

The night started with such promise for the Nationals. They pounced on Kyle Kendrick with two runs in the first, including Desmond’s 80th RBI, which matched his career high. Jimmy Rollins homered off Fister in response in the bottom of the first. Jayson Werth’s RBI single in the third and Span’s 427-foot bomb to right in the fifth put the Nationals ahead by two again.

“It’s been probably three or four years since I touched a ball like that,” Span said.

But Fister, again, could not protect a lead or save the Nationals. Afterward, he packed clothes into an army-green duffel bag. As he stood up, Fister bonked his head on an open door to a cubby in his locker. Fister stared straight ahead, refusing to show if it hurt.

“You have to forget about today or yesterday and go and get the next one,” Fister said. “You have to have amnesia. You have to be able to forget about it and move on.”