But reliever Ryan Mattheus needed just two pitches to get out of the jam. Craig grounded into a forceout at the plate, then Molina bounced into an easy double play.
And on the first pitch of the eighth, Cardinals rookie shortstop Pete Kozma misplayed Michael Morse's grounder. Ian Desmond followed that error with a hit and, two outs later, pinch hitter Tyler Moore slapped a two-strike single to right for a two-run single.
"It's baseball," Cardinals outfielder Matt Holliday said. "They got a guy who throws groundballs and he came in and got two of them. You've got two of the best hitters in the league coming up. It just didn't work out."
The Nationals, who had never come close to making the playoffs since moving from Montreal for the 2005 season, overcame a wild outing by 21-game winner Gio Gonzalez to start the NL division series.
Mattheus got the win for his two-pitch, three-out seventh, and Drew Storen pitched a perfect ninth for the save. Mitchell Boggs, victimized by Kozma's error in the eighth, took the loss.
The NL East champion Nationals led the majors with 98 wins this season, and brought postseason baseball to Washington for the first time since 1933. The Nats go for a 2-0 series lead Monday when Jordan Zimmermann opposes Jaime Garcia.
"This team is not hanging our heads," St. Louis starter Adam Wainwright said. "We can come back and win this easily."
The Cardinals made it to the best-of-five division series by beating Atlanta in the wild-card matchup Friday. But St. Louis wasted a 10-strikeout gem by Wainwright, failing to capitalize enough on Gonzalez's career high-tying seven walks and frustrating its towel-waving fans.
A standing room crowd of 47,078, among the largest at 7-year-old Busch Stadium, bundled up for a game that began in 54-degree chill and featured kaleidoscope late-afternoon shadows that bedeviled hitters for several innings.
Wainwright became the first Cardinals pitcher to reach double digits in strikeouts since Bob Gibson also fanned 10 to beat the Tigers in Game 4 of the 1968 World Series.
Wainwright was a 14-game winner coming off reconstructive elbow surgery that sidelined him all of 2011, with 10 of the wins coming at home. He's been a postseason ace with a microscopic 0.77 ERA and 32 strikeouts in 23 1-3 innings.
He fanned Bryce Harper and Ryan Zimmerman twice each and seventh-place hitter Espinosa all three times.
"His breaking ball really bailed him out today and kept them off-balance and had a lot of swing-and-misses and some chases and strikeouts with the breaking ball," Cardinals manager Mike Matheny said.
Gonzalez allowed just one hit in five innings, on David Freese's full-count bouncer between third and short to start the fourth. But he had trouble finding catcher Kurt Suzuki's glove.
The second inning was Gonzalez' shakiest when he allowed the Cardinals to score twice and take the lead without a hit. Gonzalez walked four of the first five hitters, putting St. Louis in position to score one run on a wild pitch and a second on Jon Jay's bases-loaded sacrifice fly.
Nationals right fielder Jayson Werth robbed Daniel Descalso of a two-run homer off with a leaping catch to keep it at 2-1 in the sixth. Descalso had a fielding gem of his own in the seventh, ranging far to his left to glove Harper's grounder and then throwing him out by a few steps.
Both pitchers were aided by the late-afternoon shadows. The narrow roof above the top of the upper deck, and lattice work beneath the roof, creates a hodge-podge of sun and shade. At one point, pitchers were throwing from sunshine into shade, a small stretch of sun then shade again.
It was little surprise there were just five singles and no runs in innings three through six, when the shadows were most prominent.
"He's hard to hit when you can see well, and even harder when you can't," Holliday said of Gonzalez. "It's hard to hit when you can't see the ball, see the spin on the ball."
NOTES: The Cardinals went 0 for 8 with runners in scoring position. ... Garcia was 4-2 with a 2.82 ERA in nine starts at home. The lefty has a 2.48 career ERA at Busch. ... Kozma committed one error in 26 games after taking over as the regular SS in September for injured Rafael Furcal.