"Huge," Nationals first baseman Adam LaRoche said afterward. "It feels like we stole one."
With the loss, which came in front of 47,078 at Busch Stadium, the Cardinals will have to win three of the next four games in order to advance past this best-of-five series.
"We had an opportunity to win this one and it didn't happen," Carlos Beltran said. "Tomorrow, we have to win. We have to leave this place with an even series."
St. Louis carried a 2-1 lead into the eighth, an advantage built up with great assistance from Gonzalez. Though the lefty allowed just one hit over five innings, his seven walks and one wild pitch staked the Cardinals to an early advantage.
But the Cards had been unable to turn more Gonzalez walks into runs. And though they carried their one-run lead into the eighth, there was a sense that momentum turned when St. Louis missed a chance to substantially pad its lead a half inning earlier.
The Cardinals opened the seventh with three straight hitters reaching. The setup seemed perfect, too, with Allen Craig, who led the Majors in batting average with runners in scoring position, at the plate and NL MVP Award candidate Yadier Molina on deck.
The bases-loaded threat had the potential to blow open the game.
Instead, it lasted a mere two pitches. Facing reliever Ryan Mattheus, Craig grounded into a first-pitch forceout.
"I don't think it was a judgment of swinging or not," Craig said. "I just needed to put a better swing on it."
Molina swung at Mattheus' first pitch, as well. The Nationals turned the inning-ending double play.
"I was just trying to be aggressive," Molina said. "I swung at a pitch off of the strike zone. When that happens, no good thing happens."
The missed opportunity became game-changing when the Nats answered by not squandering an opportunity of their own.
Kozma, who two days ago stirred the infield fly debacle in Atlanta by not making an eighth-inning catch, again found himself with unwanted attention. The eighth opened with a grounder caroming off Kozma's glove as he attempted a routine backhanded attempt.
Ian Desmond followed with his third single of the day, moved to second on a bunt and remained there as Matheny removed Mitchell Boggs with two out. Instead of letting Boggs finish out the eighth, as usual, the manager turned to lefty Marc Rzepczynski when a left-handed pinch-hitter was announced.
Nationals skipper Davey Johnson countered with right-handed Tyler Moore, who blooped a two-strike, two-run single into right field.
"I had faith that if they did make a move to remove [left-handed-hitting Chad] Tracy from the game, that Zep would be able to get out one of their young right-handed pinch-hitters," Matheny said. "It didn't work for us."
"It was just a little bit up," Rzepczynski said of the pitch that led to the go-ahead runs. "If maybe it was a little bit down, he hits it on the ground."
The Cardinals, who went 78-5 when leading after seven innings during the regular season, didn't recover from the blown save, and it cost Adam Wainwright his first win as a postseason starter.
Wainwright covered the first 5 2/3 innings, striking out 10 and limiting the damage to a lone two-out run in the second. He allowed the leadoff hitter to reach in four of the six innings he started, but routinely came up with strikeouts to wiggle out of trouble.
The right-hander became the first Cardinals pitcher to record double-digit punchouts in a postseason game since Bob Gibson struck out 10 in Game 4 of the 1968 World Series.
"I was feeling good," Wainwright said. "My fastball command kind of left me there toward the end. I was running my pitch count higher than I wanted to. But for the most part, I feel like I went out there and competed my tail off and gave it everything I had."
The Cardinals built up a lead for Wainwright without a hit off Gonzalez, who matched his career high with the seven walks. Four of them came in the second inning.
Molina took an eight-pitch walk to open the frame. With one out, walks to Daniel Descalso and Kozma loaded the bases for Wainwright.
Gonzalez's fifth pitch to Wainwright bounced to the backstop, allowing Molina to score the tying run. Wainwright walked on Gonzalez's next offering, and Jon Jay followed with a go-ahead sacrifice fly.
It took Gonzalez 37 pitches -- five of which had to be blocked in the dirt by catcher Kurt Suzuki -- to maneuver through the inning, and it wasn't until the Cardinals sent their 11th hitter of the frame to the plate that they saw a first-pitch strike. By forcing Gonzalez to throw 55 pitches in the first two frames, the Cards ensured his early exit.
"He gave us some chances with being wild," Matt Holliday said of the NL Cy Young Award candidate. "But he's tough to hit, particularly in those kinds of shadows. He's tough to hit when you can see well, and even harder when you can't."
The Cardinals, who went 21-26 in one-run games this season, do have recent memory to grab onto as they try to emerge from this precarious position. St. Louis lost Game 1 of its NLDS series against Philadelphia in 2011, before rallying en route to a World Series title.
"We've been in this spot before," Descalso said. "We'll show up to win tomorrow. We'll be fine."