SAN DIEGO -- The San Diego Padres' Melvin Upton Jr. showed up his old team and trumped James Shields' stellar pitching.

Shields pitched six shutout innings, but Upton Jr. hit a pair of two-run homers as San Diego thumped the Atlanta Braves, 9-0, on Tuesday.

"Mel's been getting some key hits and contributing to wins, but that was a breakout performance," Padres interim manager Pat Murphy said. "It's great to see. It's much-needed for him. It was good for him."

Shields (9-5) allowed five hits, walked two and struck out seven as the Braves lost their ninth straight at Petco Park. It was Shields' second win in 14 starts and his first at home in more than a month.

"I've seen his velocity a lot better than today for whatever reason, but he didn't give in," Braves manager Fredi Gonzalez said. "He changed speeds really, really well, especially with people on base."

It was the center fielder Upton's seventh multi-homer game, with his second home run to left field coming in the seventh.

"I didn't see that coming, but I felt pretty good at the plate." he said. "I believe in what I'm doing. It was just good to show a flash of it today."

Shields was appreciative of the support of Upton.

"A lot of people don't understand, this guy's been taking some really good swings the last month," Shields said. "Unfortunately he hasn't gotten a crazy amount of hits, but he's been taking really good at-bats, he's been taking his walks, which I'm most impressed about. He's showing patience at the plate and things are coming together for him."

San Diego hit two homers in its five-run sixth inning in which it sent 11 batters to the plate against three Braves relievers.

Second baseman Yangervis Solarte hit a three-run shot into the second deck, which followed Upton's two-run blast.

Also in the inning, left fielder Justin Upton doubled, shortstop Alexi Amarista singled, with second baseman Cory Spangenberg and pinch-hitter Brett Wallace drawing walks.

Matt Wisler (5-3) worked five innings and was charged with two runs, six hits and two walks. The former Padre walked two.

"I definitely have to be more efficient on the mound," Wisler said. "I thought I made some strides the last couple of innings after having almost 50 pitches in the first two and then after that I thought I got down to like 15 pitches an inning. I've got to attack guys early in the count, get ahead, and I haven't done that as much as I should have been lately."

Wisler also took a line drive off his right triceps from a Shields line drive but he said he was fine.

"It definitely could be worse," he said. "It definitely will be a little sore."

After Shields stifled the Braves, Odrisamer Despaigne and Kevin Quackenbush blanked them the final three innings.

Atlanta has lost 17 of their past 25 games and are 11-24 since July 8.

The Padres stretched their lead in the fourth to 2-0 on an RBI single by center fielder Melvin Upton Jr. He knocked in catcher Derek Norris after his double.

The Braves loaded the bases in the fourth when catcher A.J. Pierzynski walked before base hits by third baseman Adonis Garcia and second baseman Jace Peterson. But Shields struck out first baseman Joey Terdoslavich and induced shortstop Andrelton Simmons to hit into a 6-4-3 double play, with first baseman Yonder Alonso making a nifty scoop on second baseman Cory Spangenberg's relay.

"We had a chance to get Shields with the bases loaded and he wiggled out of it," Gonzalez said. "Instead of tying the score or being ahead we never got a run."

Wisler escaped from a jam in the first when he walked third baseman Yangervis Solarte and left fielder Justin Upton. But Wisler wasn't as fortunate in the third.

Spangenberg laced a one-out triple to right-center field. Right fielder Matt Kemp followed with a sacrifice fly to center for a 1-0 Padres lead.

In the second, the Braves wasted a leadoff double by Garcia as Shields countered with two strikeouts and a ground out.

But a tight game turned into a larger.

"You remove the sixth inning from the box score and it's a good game," Gonzalez said. "It's 2-0 at the time and you feel like you are bringing those guys in to keep it like that. Then it's a battle of the bullpen and we didn't get it done today.

NOTES: The Padres traded OF Will Venable to the Rangers for minor league C Marcus Greene Jr. and a player to be named later. ... INF Jedd Gyorko was rested after his first start at shortstop. ... INF Alexi Amarista started his team-high 73rd game at short. ... Braves 1B Freddie Freeman (oblique, wrist) will be activated off the disabled list for Wednesday's game. ... SS Andrelton Simmons hasn't committed an error since June 15.