After hitting .221 for the New York Yankees in 2004 and .232 for the Mets in 2003, Clark signed a one-year deal with Arizona for only $750,000. Vargas, meanwhile, was claimed by the Diamondbacks on waivers from Washington on June 3, and he has become one of Arizona's top starters.
"I don't know where we'd be without him," Arizona manager Bob Melvin said.
Melvin said the turnaround for Vargas "seems to be his confidence, and knowing what he's going to do every five days."
Vargas (6-6) walked two and struck out five. He added a bases-loaded single in the sixth for his first two career RBI.
"When I pitched in Washington it was so hard for me," Vargas said. "If I give up one or two runs, they take me out of the game. I have the opportunity here."
Clark hit two-run homers in the first and third innings, giving him 21 -- his best mark since hitting 31 for Detroit in 1999.
"He's been incredible all year," said Shawn Green, who added three hits, including his 17th homer. "From the latter part of spring training on, he's been a machine. I've never seen a guy with as limited number of at-bats put up the numbers he's been putting up, with consistency and in key situations."
With only 228 at-bats, Clark is second on the team in homers and third with 61 RBI. Clark, hitting .325, delivered his first multihomer game of the season exactly one week after he signed a two-year extension with Arizona worth about $2 million.
"That guy's unbelievable," Braves first baseman Adam LaRoche said of the 6-foot-7 Clark. "That's some serious pop. The guy's huge. I felt like a little girl standing next to him at first base. No offense to girls."
Vargas is 6-3 with Arizona. He has not allowed more than three earned runs in nine straight starts, including two against the Braves. He held Atlanta to seven hits and one run in seven innings in Arizona's 6-5 win in 10 innings on July 22 in Phoenix.
"Somebody's done a terrific job with that kid," Braves manager Bobby Cox said. "He had a lot of pitches tonight, but they were quality. He had a purpose for every one of them. Looks like he knows what he's doing out there pretty well."
The Diamondbacks led 5-0 after three innings against Braves starter Jorge Sosa (7-2).
One day after Cox gave Sosa a vote of confidence by sending a more established starter, Horacio Ramirez, to the bullpen to make room for the returns of Mike Hampton and John Thomson from the disabled list, Sosa suffered his first loss since June 23 against Florida.
Sosa gave up seven hits and five runs in five innings. He had been 5-1 with a 2.25 ERA in his first 11 starts.
After Tracy hit a one-out double in the first inning, Clark gave Arizona a 2-0 lead with his first homer of the game, a 412-foot drive to right.
Green's leadoff homer in the second inning pushed the lead to 3-0. Luis Gonzalez hit a two-out single in the third and Clark hit an opposite-field homer to left-center off Sosa for a 5-0 lead.
The Diamondbacks added three runs in the sixth. Rookie reliever Kyle Davies gave up singles to Troy Glaus and Green before issuing an intentional walk to Kelly Stinnett to load the bases for Vargas with two outs.
Vargas punched a bloop single to shallow center to drive in two runs. Craig Counsell followed with another bloop single to center to drive in Stinnett for an 8-0 lead.
Arizona reliever Greg Aquino left the game after he was struck in his right forearm by Rafael Furcal's line drive in the eighth inning. Aquino threw out Furcal and was replaced by Buddy Groom, who recorded the final out of the inning and worked the ninth. Aquino was taken for X-rays after the game.
- Both teams announced roster moves after the game. The Braves will send Davies to Triple-A Richmond on Saturday when they activate RHP John Thomson. The Diamondbacks will send C Koyie Hill to Triple-A Tucson to make room on the roster for RHP Russ Ortiz. The team also moved LHP Shawn Estes to the 60-day DL.
- Clark has four homers in the last eight games.
- The teams played through light rain most of the game but there were no delays.
- Green made a diving catch of a drive hit by Furcal in deep center in the sixth inning.