Gio Gonzalez heads to the dugout after allowing four runs in the fifth inning. They were the only runs he gave up in six innings. (Jonathan Newton/THE WASHINGTON POST)

Once this season of high expectations ends — with a growing likelihood of those expectations being unmet — the Washington Nationals will have time to reflect on the chances that slipped through their fingers. For months, they underperformed. When time grew short, they rallied. But Saturday night at Nationals Park, with urgency still very much required, they fell short in what could be their costliest defeat of the season.

The 5-4 loss, coupled with victories from the teams above them in the wild-card chase, snapped a seven-game win streak and left the Nationals 51 / 2 games out of the second wild card with 14 games remaining. According to the Nats enter play Sunday with a 1.8 percent chance of making the playoffs.

The Nationals mounted a spirited comeback after trailing 5-1 in the seventh inning, but couldn’t deliver the final blow. Wilson Ramos struck out on a questionable called third strike call by home plate umpire Jim Joyce to end a seventh-inning rally. Denard Span’s chopper up the middle in the eighth could have tied the score if 6-foot-4 reliever Jake Diekman was a few inches shorter. The Phillies intentionally put the go-ahead run on base, Bryce Harper, with two outs in the ninth inning and their strategy worked.

Much like the rest of their season, the Nationals’ surge was too little, too late.

“We need wins,” said Span, who collected three hits to extend his hitting streak to 25 games. “We can’t lose too many more times.”

The Nationals’ season is not over, nor have they been mathematically eliminated. But Saturday’s loss — a game in which they stranded 11 base runners and in which pitching miscues in two innings doomed them – felt like it could be the decisive blow. The Nationals would need to go 11-3 and hope the Reds go 5-8 just to force a one-game playoff.

Despite the odds, a somber Nationals clubhouse remained defiant.

“It’s not over yet,” starter Gio Gonzalez said. “No one has told us this game is done.”

“We’re playing with house money,” added shortstop Ian Desmond. “Everyone kind of wrote us off, and we’re fighting our way back in. Just keep on playing and what will be will be.”

Gonzalez pitched four strong innings to start the game, but his command slipped in the fifth inning. John Mayberry mashed a high fastball to left for a solo home run. The Phillies took a 4-1 lead when Gonzalez allowed a two-out, three-run double to right to Carlos Ruiz.

“One pitch,” Gonzalez said. “Fastball away and he just put it right there on the spot. It hangs in there a little bit longer, [Jayson Werth] gets an out.”

Struggling left-handed reliever Ian Krol allowed the Phillies to push the lead to 5-1 in the seventh when he allowed a double, fired a wild pitch and then gave up an RBI single. In the bottom of the frame, the Nationals rallied.

“I had no doubt in my mind that we were going to come back and win that game,” Desmond said.

Pinch hitter Scott Hairston led off the bottom of the seventh inning with a single to left. Span followed with his third hit of the game and Ryan Zimmerman loaded the bases with a single that chased starter Cole Hamels. Werth grounded out into a fielder’s choice, with third baseman Cody Asche getting Hairston at the plate. Desmond trimmed the deficit to 5-2 when he lifted a ball to center field that was deep enough to score Span.

Up to the plate came Harper. Phillies interim manager Ryne Sandberg brought in left-hander Cesar Jimenez, and Harper blooped a single to center field. Werth rounded third and didn’t stop running. He scored and Harper slid into second base safely. Harper then stole third base, catching Asche far off the base.

Sandberg called on the fourth pitcher of the inning, B.J. Rosenberg, to face Ramos. The catcher fouled off four pitches. On the seventh pitch of the at-bat, he held off on a Rosenberg slider that moved him off the plate and broke inside. Ruiz caught the ball near the ground and couldn’t frame it, but Joyce rang up Ramos. The catcher was unhappy with the call, and appeared to express his frustration to Joyce before walking into the dugout.

Johnson later said Joyce admitted he may have blown the call.

“He knew he missed it,” Johnson said. “But that’s part of baseball. But we had a lot of chances and had the right guys up.”

In the eighth inning, pinch hitter Chad Tracy drew a walk and Johnson replaced him with pinch-runner Jeff Kobernus. With Kobernus at second base with two outs, Span chopped a grounder toward the mound. Diekman jumped for the ball, snagged it and tossed it to first to end the threat.

“I thought it was going to hit off his glove or tip off his glove,” Span said. “I know with Kobernus running that if it would have done that, he probably would have scored on that. Diekman is already 6-4 and he jumped off that mound pretty good and made a good play.”

The Nationals didn’t go quietly in the ninth. Zimmerman led off with a double laced to left off closer Jonathan Papelbon. The heart of the Nationals’ lineup followed. Werth lined out to right and Desmond popped out to right.

With two outs, Sandberg elected to intentionally walk Harper to face Ramos. The Phillies put themselves in a precarious situation, but Papelbon got Ramos to hit a grounder up the middle. Shortstop Jimmy Rollins snared the ball and threw Ramos out at first.

“We’ve come this far,” Span said. “Nobody expected us to be where we are now two weeks ago. So we just gotta keep battling. We’re playing good baseball. We can’t get too down on ourselves. We gotta regroup and be ready to come back [Sunday] and get a win and get back on the right track.”