Chris Denorfia led off the 12th with a single off Kris Medlen (6-2), Atlanta's seventh pitcher. Denorfia stole second base as Tony Gwynn Jr. struck out for the second out. An intentional walk to Oscar Salazar put runners on first and second for Hundley, who pinch hit for Tim Stauffer (3-1).
Hundley's double down the left-field line made it 6-4.
Heath Bell earned his 27th save with three strikeouts in the bottom of the 12th to end a game that lasted 4 hours, 13 minutes.
It was the fourth blown save for Wagner, who couldn't hold a 4-2 lead in the ninth. The Padres rallied with Scott Hairston's pinch-hit homer, a single by Jerry Hairston and Yorvit Torrealba's tying double.
The Braves led 4-2 after Brian McCann's two-run homer capped a four-run third inning.
In Los Angeles, Chad Billingsley pitched a shutout of San Francisco to give Los Angeles its first win in seven games.
Billingsley (8-5) threw 125 pitches to earn his second career shutout and third complete game.
Casey Blake homered in the second inning to end the Dodgers season-worst losing skid.
San Francisco starter Barry Zito (8-5) gave up six hits in 7 1-3 innings.
In St. Louis, rookie Jaime Garcia stymied Philadelphia for seven innings as St. Louis made it eight straight wins.
Garcia (9-4) lowered his ERA to 2.21, rebounding from two iffy starts in which he gave up 17 hits in 5 2-3 innings, although he gave up only four earned runs.
Matt Holliday's homer leading off the bottom of the seventh was the go-ahead hit for the NL Central leaders, whose streak is the franchise's best since winning eight straight in 2004.
St. Louis beat the two-time defending NL champions three straight games by a 20-6 total.
The Phillies have lost six of seven since the All-Star break and are only two games above .500. Starter Joe Blanton (3-6) gave up three runs in the eighth.
In Miami, Gaby Sanchez hit a three-run homer to lift Florida over Colorado.
Marlins starter Ricky Nolasco (10-7) pitched eight innings, allowing four hits while striking out eight. He has 10 wins each of the past three seasons.
Rockies starter Jason Hammel (7-5) fell to 0-3 against the Marlins in his career as he allowed five runs in seven innings.
In Cincinnati, Stephen Strasburg tamed the NL's top offense as Washington downed Cincinnati.
A day after he turned 22, Strasburg (5-2) pitched beyond his years again, passing one of his toughest tests, while getting some belated run support.
Strasburg struck out seven and gave up three runs in 5 1-3 innings, out dueling Bronson Arroyo (10-5), who had allowed only three runs in his past three starts, winning them all.
Arroyo went 5 2-3 innings, allowing seven runs.
In Phoenix, a pinch-hit RBI single in the 14th inning by Chris Snyder gave the Arizona a three-game sweep of fading New York.
Snyder, the last position player available for Arizona, hit a pitch from Fernando Nieve (2-4) over the head of the left fielder to bring home Justin Upton, who had led off the inning with a double.
The Mets fell to 1-6 on their 10-game Western trip and remained 6_ games behind first-place Atlanta in the NL East. They finish the trip with three games against the Dodgers in Los Angeles starting Friday.
Five Arizona relievers shut out New York on one hit over the last eight innings. Blaine Boyer (2-2) was perfect over the final two, striking out two, to get the victory.
In Chicago, pinch-hitter Jason Michaels delivered a two-out, two-run double in the top of the 12th inning to give Houston victory over Chicago.
Jeff Keppinger and Chris Johnson started the 12th with consecutive singles. After Keppinger was forced out at third when Jason Castro bunted back to Bob Howry (1-3), James Russell relieved and Michael Bourn's grounder moved the runners to second and third.
Michaels hit Jeff Stevens, the seventh Chicago reliever, with a drive into the alley in left-center. Angel Sanchez then singled in Michaels to make it 4-1.
In the bottom of the 12th, Geovany Soto connected for a two-out, two-run homer off Gustavo Chacin in the bottom half, pulling the Cubs within one. Ryan Theriot singled and pinch-hitter Jeff Baker walked before Tyler Colvin lined out to right, giving Chacin his first career save.
Chicago stranded 16 runners.
Brandon Lyon (6-4) pitched two scoreless innings to get the win.
In Pittsburgh, Pedro Alvarez hit two home runs for the second consecutive game for Pittsburgh, which routed Milwaukee.
The Pirates' rookie hit a two-run homer to center in the fifth and a solo shot off the right-field pole in the eighth.
Randy Wolf (7-9) allowed a career-worst 12 runs in 5 2-3 innings. It was the third time in four games that a Brewers starter had given up more than 10 runs.
Pittsburgh starter Zach Duke (4-9) allowed two earned runs in six-plus innings.
