ST. LOUIS -- Brandon Moss said after Tuesday night's game that Busch Stadium plays bigger than any ball park he's ever played in, but it couldn't hold his biggest hit of the year.

The St. Louis Cardinals first baseman capped another wild comeback with a three-run homer in the bottom of the ninth inning, leading them to an 8-5 win over the Washington Nationals.

Moss clubbed a 1-0 fastball from reliever Casey Janssen (1-4) 424 feet to the grassy knoll behind the center field wall for his third homer since St. Louis acquired him July 30 from Cleveland.

"If that one wasn't going to go," Moss said, "none of them would ever go. I don't even remember my trip around the bases."

Pinch-hitter Cody Stanley doubled with two outs and center fielder Tommy Pham coaxed a walk after falling behind 0-2 to set the stage for the Cardinals' latest dramatic rally. They also trailed Washington 5-3 on Monday night before scoring five two-out runs in the bottom of the seventh for an 8-5 decision.

It was St. Louis' ninth walk-off win of the year and its 34th come-from-behind triumph, pushing it to a season-high 40 games over .500 at 86-46.

"I think their style of play every single day deserves acknowledgment," Cardinals manager Mike Matheny said. "They figure out a way to make it happen."

Especially when the Nationals arrive in town. St. Louis has beaten them 20 times in the last 22 games under the Gateway Arch, dating back to 2008, and this one might have been the most improbable of all.

Washington led almost the entire game after scoring four runs in the third -- second baseman Anthony Rendon doubled home a pair of runs, right fielder Bryce Harper scored Rendon with a sacrifice fly and first baseman Ryan Zimmerman clouted a solo homer to left-center -- and still owned a 5-3 edge as the bottom of the eighth started.

But the Cardinals tied it with two runs on just one hit -- Pham's leadoff single. Reliever Drew Storen propped them up with a wild throw to third on a sacrifice bunt by pinch-hitter Greg Garcia, plating Pham, and a double play grounder by right fielder Stephen Piscotty scored Moss with the equalizer.

The Nationals (66-65) then stranded two in their half of the ninth as reliever Mitch Harris (2-1) induced a fly-out from shortstop Ian Desmond, setting the stage for Moss' fifth career walk-off homer.

As St. Louis upped its National League Central lead over Pittsburgh, a 7-4 loser in Milwaukee, to six games, Washington failed to cut into the New York Mets' 6 1/2-game lead in the NL East.

"Time isn't on our side," Janssen said, "and we need to continue to play well and find a way to get back into this thing."

After two scoreless innings, neither starter survived a 49-minute third inning.

Washington knocked out St. Louis left-hander Marco Gonzales with four runs and six hits in its half of the inning. Second baseman Anthony Rendon initiated scoring with a two-run double, followed by a sacrifice fly from right fielder Bryce Harper and a solo homer to left-center by first baseman Ryan Zimmerman.

But Nationals right-hander Joe Ross gave back three in the Cardinals' third on just one hit, a two-out RBI single by shortstop Jhonny Peralta. Ross walked second baseman Kolten Wong with the bases loaded, then reliever Doug Fister forced in the last run by plunking first baseman Mark Reynolds.

Both pitchers lasted 2 2/3 innings. Gonzales allowed seven hits and four runs with a walk and a strikeout. Ross permitted just Peralta's hit, but was charged with three runs after issuing six walks while fanning three.

While Washington lamented a big-time missed opportunity, St. Louis relished its latest stirring win.

"Thank goodness that went over the wall," Moss summed up.

NOTES: Washington reinstated 2B Dan Uggla (back spasms) from a rehab assignment, and recalled C Pedro Severino from Double-A Harrisburg as well as LHP Sammy Solis from Triple-A Syracuse. ... St. Louis recalled LHP Marco Gonzales, C Cody Stanley and RHP Mitch Harris from Triple-A Memphis. Gonzales started Tuesday night. ... The Nationals transferred RHP David Carpenter (right shoulder) to the 60-day DL, effectively ending his season. Carpenter allowed just one run in six innings, covering eight outings, with Washington.