PHOENIX -- As a gray-haired man himself, Tony Clark likes to joke around with manager Bob Melvin about some of the gray hairs he's sprouted managing a D-backs club with a penchant for one-run games.

Melvin did not mind the stress on Sunday, because it came with another come-from-behind one-run victory when Arizona beat St. Louis, 6-5, at Chase Field.

This time, the old graybeard at first base made up the difference, smacking a go-ahead two-run double in the seventh for an Arizona squad that played its 49th one-run game on Sunday.

"I think down the stretch, as we continue to play against quality ball clubs, the games are going to continue to be close, so having had some success in one-run or two-run ball games, I think, has made a big difference for us at this point," Clark said.

The victory, the D-backs' fifth in a row after falling out of first place on Monday, moved Arizona three games ahead of San Diego in the National League West and five games up on a playoff spot.

Before the veteran Clark had a chance to knock in the eventual winning runs, the youngest member of the Diamondbacks, 20-year-old Justin Upton, smashed a game-tying two-run homer off Ryan Franklin (4-3) to start a four-run seventh. Upton, who had not homered since Aug. 7, nailed a fastball to swing the momentum in a game the D-backs had not scored in since the second.

Helping Arizona win a crucial game in a pennant race marks quite a journey for the former No. 1 overall Draft pick, as Upton started the season in Class A Visalia before moving on to Double-A Mobile and eventually the Majors. For his efforts in the Minors, he earned the organization's Minor League Player of the Year Award on the same day he hit a game-changing homer.

"It's a good feeling going from that and coming here and being able to contribute," Upton said. "Hopefully, I can contribute some more."

Upton's day could have come to an end when he ran into the wall trying to chase down a two-run triple off the bat of Miguel Cairo in the third. Upton banged his knee on the play, but stayed in the game.

That set up his at-bat against Franklin, a tough righty who entered the contest with a 2.03 ERA, which Melvin said re-energized his club.

"His at-bats were good all day, really," Melvin said. "They've been a little better than maybe some of the performances would suggest, but that's off Franklin right there, especially a right-hander, he hasn't given up anything all year. The one ball he gets up, he's all over it, so we were opportunistic on the balls that they did give us a chance to lay a barrel on."

For the second straight game, the D-backs bullpen held St. Louis down to make the heroics of Upton and Clark possible.

A day after giving up one run in 6 1/3 innings, the 'pen allowed one run in five innings. Yusmeiro Petit (3-4) gave up one hit in two scoreless innings, and Jose Valverde closed the game with his 45th save, Arizona's fourth straight game that he has saved.

Valverde, however, did not make it easy for himself. After retiring the first two batters, he allowed the next four hitters to reach before ending the contest with the bases loaded.

"We were really fortunate today to battle back," Clark said, "and our guys coming out of the bullpen did a really fine job keeping the game close and giving us an opportunity."

That effort made up for starter Doug Davis struggling through a poor third inning, in which he gave up all four runs and five of the seven hits he allowed in his four innings. Davis had thrown quality starts in 10 of his last 12 outings, but the comeback extended the streak of Arizona wins in 11 of Davis' last 12 starts.

"This is one of those games where [Davis] just didn't have his good rhythm, command all of that," Melvin said. "Everyone who came in behind him kept us there, and our offense came back again, like we've seen here quite a few times this homestand. [This] ends up being a great win, again."

The win capped a series sweep against the Cardinals, a team Arizona lost three of four from in July, with the D-backs coming back from a multiple-run deficit to win the previous two. As Arizona builds toward a possible playoff berth, beating the defending World Series champions could provide the D-backs with a nice boost.

"This is a team we've always had trouble with, in my years here," Melvin said. "To finally come back and not only beat them, but sweep them here, I think, is another confidence builder. It's good to beat a team like this, especially the way we've been playing building up to this."