ST. LOUIS — Rookies in the postseason, the Washington Nationals played like poised veterans.
The Nationals escaped a bases-loaded jam in the seventh inning, Tyler Moore blooped a two-out, two-run single in the eighth, and Washington beat the defending World Series champion St. Louis Cardinals, 3-2, Sunday in a National League Division Series opener.
They have just four players with postseason experience on the roster. But they have the lead.
‘‘Not many people have probably watched too many Nationals games, but we have a great starting rotation and a great bullpen,’’ said Ian Desmond, who singled for his third hit in the go-ahead rally. ‘‘They keep us in the ballgame and some timely hits from this kid [Moore], and the rest of the guys coming off the bench, that’s really been the formula.’’
The Nationals, who had never come close to making the playoffs since moving from Montreal for the 2005 season, overcame a wild start by 21-game winner Gio Gonzalez. They limited the Cardinals to three hits.
‘‘All the credit in the world goes to the bullpen,’’ Gonzalez said. ‘‘I’ve been saying it all year. The reason why we’ve been so successful is these guys come in and shut it down.’’
Rookie Ryan Mattheus needed just two pitches to bail out the Nationals in the seventh with St. Louis ahead, 2-1. Moore, another rookie, put them ahead soon after that, Tyler Clippard worked around an error in the eighth, and Drew Storen saved it with a 1-2-3 ninth.
The NL East champion Nationals led the majors with 98 wins, and brought postseason baseball to Washington for the first time since 1933. They 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. But St. Louis wasted a 10-strikeout gem by Wainwright, failing to capitalize enough on Gonzalez’s career high-tying seven walks.
Mattheus diffused a bases-loaded, no-out threat in the seventh, getting cleanup man Allen Craig to ground into a force out at the plate and then inducing a double-play grounder from Yadier Molina. Craig led the NL with a .400 average with runners in scoring position and Molina batted .321 in those situations.
‘‘It was a big moment,’’ Mattheus said. ‘‘It gave us life. The guys said, ‘Hey, we can win this ballgame.’ ’’
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.
‘‘It was pretty bad, but you have to make adjustments and that’s what I did,’’ Molina said. ‘‘But what are you going to do? Quit? No.’’
No. 3 hitter Matt Holliday chimed in his complaints about facing Gonzalez: ‘‘He’s hard to hit when you can see well and even harder when you can’t.’’
Rookie shortstop Pete Kozma misplayed Michael Morse’s grounder for an error to open the eighth and set up the Nationals’ go-ahead rally. Desmond followed with a single off Mitchell Boggs, putting runners at the corners.
Danny Espinsoa sacrificed, leaving runners at second and third, and Kurt Suzuki struck out. In a series of moves, the Nationals sent up Chad Tracy to pinch hit, the Cardinals switched to lefty Marc Rzepczynski, and Washington subbed in Moore, who had two of their three pinch homers this season.
Rzepczynski pretty much hit his location but Moore poked it to right field and both runners scored easily.