PHOENIX -- The D-backs could have trudged toward Boston and Detroit after another defeat, following another blown game by their bullpen and milling over missed opportunities on a 10-game homestand.

If not for Chris Young.

Arizona's center fielder made up for his club's 12th blown save of the season on Sunday afternoon by lifting a bottom-of-the-ninth Kyle McClellan fastball just beyond the left-center-field fence. The club's first walk-off home run since Chad Tracy accomplished the feat in June 2008 cemented a 7-5 comeback win over the visiting St. Louis Cardinals.

"I knew it had a chance," Young said of his third career walk-off blast; the other two came in 2007. "I was yelling at it, hoping it would get up, and luckily it did."

With its second consecutive victory, Arizona clinched a winning (6-4) homestand entering a stiff six-game test that begins at Fenway Park on Tuesday. The D-backs haven't won a road game since May 17, but Sunday's stylish finish can only prove positive.

And you-know-who was the cause. About four hours after unofficially ranking Young fourth among his team's All-Star candidates, manager A.J. Hinch discussed Young's climb back from the Minor Leagues a season ago and his marked improvement this year (.277 batting average, 12 home runs, 44 RBIs).

"He's getting good pitches, and he's not missing them," Hinch said. "He's put a lot on his shoulders, and he's responded well, so I'm very happy for him for this moment."

There was a string of tense moments Sunday afternoon.

Edwin Jackson and his defense provided many of them early on, including a pair of double plays that halted early would-be Cardinals rallies. In the first, Mark Reynolds grabbed Albert Pujols' popup behind third base then threw across the diamond to pick off Colby Rasmus. And, in the third, right fielder Gerardo Parra charged in to capture Felipe Lopez's liner before throwing a dart behind Chris Carpenter, who had reached via single.

The first baseman on the receiving end of those two well-executed plays again provided much of the lineup's output. On a hanging 1-2 Carpenter curveball in the second, LaRoche, who busted out of an 0-for-14 skid with six hits and seven RBIs in the three-game series, doubled home Kelly Johnson (single) and Reynolds (double) for Arizona's early 2-0 lead.

And Young added a third run in the fourth with a solo blast, his third this month.

"I was talking to Justin [Upton] in the first inning, and I felt terrible," Young recalled of facing Cardinals' starter Chris Carpenter. "He went into the video room, looked up something for me, and I tried to make an adjustment as the game went on."

Of course, that 3-0 lead was far from safe.

Jackson exited with two outs in the seventh and St. Louis runners on second and third base, leaving reliever Aaron Heilman to face Pujols. Three pitches later, a broken-bat blooper past third base plated two. Then Heilman induced Matt Holliday's groundout to short, protecting his club's one-run lead.

"I felt like I made a good pitch," Heilman said. "Not much more you can do when the ball falls right on the line. He's a pretty good hitter." But closer Chad Qualls, as he has often this season, made things too interesting for his own fans late in the game. Qualls yielded four successive hits, including RBI singles authored by Pujols and Randy Winn. He gave way to Esmerling Vasquez, whose wild pitch to the first batter he faced allowed Pujols to scamper home for the game-tying run. Vasquez (1-2) was credited with the blown save. but got the win shortly thereafter.

One pitch after Montero's two-out poke in the bottom of the ultimate inning came the moment that made all the others moot.

"You try to forget about what happened before, go into the inning like it was 5-5 the entire time, and when you're the home team, you have the advantage because you get to hit last," Young summed up. "And have a chance to walk 'em off -- and that's always exciting."