Stephen Strasburg is crushed after surrendering a game-tying two-run home run to Chicago’s Donnie Murphy in the bottom of the ninth. (Charles Rex Arbogast/Associated Press)

Stephen Strasburg was stunned. He crouched next to the mound. He stared back at the left field bleachers, where Donnie Murphy’s game-tying two-run home run had just landed. Strasburg was two strikes away from firing his second complete game in three starts. Instead, he hung a 1-1 curveball to Murphy, who deposited the pitch into the glove of a Cubs fan in the first row of the stands.

The game was tied, and in a Washington Nationals season overflowing with squandered opportunities and low moments, this certainly felt like one of the worst. For the better part of eight innings, Strasburg was dominant. But his win evaporated in the span of four batters.

The Nationals scratched out a run in the 13th inning to defeat the Cubs, 5-4, and move to one game under .500. Chad Tracy’s 45-foot dribbler with one out scored Denard Span with the decisive run. Because Rafael Soriano completed the ninth, the Nationals turned to Drew Storen in the 13th, and he earned the save with an inning-ending double play.

“It’s not pretty, but sometimes you don’t need to be,” Tracy said. “You just need something to happen.”

Four innings prior, Strasburg took the mound in the bottom of the ninth having thrown just 96 pitches. Strasburg was coming off the shortest start of his career, having faced only seven batters in his previous outing, a wild appearance in which he was ejected in the second inning in Atlanta for hitting a batter and then throwing behind another.

The Post's Jonathan Forsythe talks with Nationals beat writer Adam Kilgore about why the Nationals have struggled this season. (The Washington Post)

Strasburg had an early lead and mowed through the Cubs’ lineup. He allowed only one run on four hits over the first eight innings. “He pitched a great game,” Manager Davey Johnson said.

For eight innings, Johnson’s point was beyond debate. Then Strasburg unraveled. With one out, he gave up a single to catcher Dioner Navarro. The next batter, right fielder Nate Schierholtz, rolled over a change-up toward second baseman Steve Lombardozzi. He and shortstop Anthony Rendon tried to turn two, but Schierholtz beat the relay. He then took second on defensive indifference.

Strasburg and catcher Wilson Ramos teamed up to nab two base runners earlier in the game, something the pitcher has made a concerted effort on recently. But in this spot, the two were more focused on the batter. Center fielder Junior Lake then smacked a ball deep into the hole at short. Rendon, a third-baseman-turned-second-baseman filling in for shortstop Ian Desmond (stiff back), gloved the ball. His throw skipped past first baseman Tyler Moore and bounced off the tarp, allowing Schierholtz to score.

“You feel terrible,” Rendon said. “Obviously I had a little slip-up there, but that’s no excuse. I still should’ve made that play. If that happened, that’s not how our season would’ve went or my season would’ve went, so it’s like it had to happen almost.”

Strasburg, visibly upset, still had to deal with Murphy. Entering the at-bat, three of Murphy’s seven home runs had come in this four-game series. Strasburg fed him two 96-mph fastballs, the first a ball, the second a swing and miss. Then came Strasburg’s curveball, an out pitch for him Thursday that had helped him strike out eight batters. This one stayed over the heart of the plate and didn’t have the same bite. Murphy waited on it. Strasburg could only watch as it carried over the wall at Wrigley Field.

“I feel like I can look at it two ways: I can look at that last inning or I can look at all the other innings where I was pitching really well,” Strasburg said. “So I’m gonna focus on the positive. Kind of the story of the year, to be honest. The guy Murphy, I had my way with him all day and then he runs into a curveball. So it is what it is.”

Johnson took issue with the pitch selection.

“If he just locates the fastball nobody is going to hit him in that part of the game,” he said. “He threw a decent curveball, but it was up and over the heart of the plate. If he bears it down, he gets by with it. . . . That’s just part of the learning curve. He’s going to be awfully good. He is awfully good. He’s only going to get better and learn from that.”

Before the disintegration, Strasburg was almost unhittable. The lone hit in the first four innings was a bloop single by Navarro. He was staked to an early lead thanks to third baseman Ryan Zimmerman, who hit the first pitch he saw from Cubs left-handed starter Travis Wood to right-center for a solo home run.

In the second, Strasburg added to the lead with an RBI single in a tough at-bat in which he fouled off four pitches. Rendon’s sacrifice fly scored another run. In the seventh, Lombardozzi’s first home run of the season, the first of his career as a right-handed hitter, made it 4-0.

Strasburg allowed his first run of the game in the eighth inning. Left fielder Brian Bogusevic smashed a first-pitch fastball to right-center, the alley where the ball carries here during the summer. With one out, pinch hitter Cole Gillespie singled to left. Strasburg sat at 93 pitches and Tyler Clippard began warming in the bullpen. But Strasburg buckled down and induced a double-play grounder to third to get out of the inning.

Clippard sat down. Strasburg hit for himself in the ninth. He was determined to finish this game, as Johnson had predicted earlier in the day. A hanging curveball dashed those hopes.

The victory would not be salvaged until the 13th. The Nationals put the leadoff hitter on base in three of the four extra innings but didn’t score until Span opened the 13th with a double off Michael Bowden, the sixth Cubs pitcher. Lombardozzi’s sacrifice bunt moved Span to third. Tracy’s swinging bunt of a 2-2 slider scored what proved to be the winning run.

“I know he was on the after-game show as the hero,” Johnson said of Tracy. “But we gotta do better than that. That gave me a heart attack. Good thing we got a track star running on third base. A win is a win.”