Byrnes failed to come through with the bases loaded in the third inning, but didn't waste another chance in the fifth against Tom Glavine. Byrnes figured he was overdue for a grand slam.
"I went 100 [at-bats] without hitting one," he said.
Actually, Byrnes was 15-for-67 (.224) with the bases loaded in his career before the homer gave Arizona a 6-3 lead. He was 0-for-2 and had left four runners on base before his slam.
"I had left a small army on base," Byrnes said. "I was scrapping at that point."
The slumping Byrnes needed the big hit. He was batting .135 (10-for-74) in May and hit seventh for only the third time this year.
Byrnes had more troubles in his first two at-bats against Glavine. He struck out with a runner on third to end the first inning.
With Atlanta leading 3-2 in the fifth, Glavine issued back-to-back walks to Justin Upton and Snyder to load the bases for Byrnes, again with two outs. This time, Byrnes turned on a 2-2 pitch and hit a drive to left that barely cleared the wall beyond the reach of Gregor Blanco.
"I really couldn't tell whether it would get out," Byrnes said. "I was just hoping he wouldn't catch it."
It was only the second grand slam allowed by Glavine in his 22-year major league career.
"As long as it makes it over the fence, I have no issue," Arizona manager Bob Melvin said.
Young's leadoff homer also barely made it over the left-field wall. Blanco appeared to help push the ball over the fence with his glove.
Young was still seeking clarification from the umpires after rounding second on his jog around the bases.
"There was big doubt," Young said. "I thought it was a routine fly ball. I'm not lying. The wind must have got it."
But the big hit belonged to Byrnes, whose struggles were obvious to his teammates.
"He didn't get it done the first few times," Young said. "He looked horrible the first few times, but he got hold of the last one and that's all it took."
Glavine gave up six runs and five hits while walking six in 4 2/3 innings. Braves pitchers issued a season-high 11 walks.
"It was one of those days, I guess," Glavine said. "We don't typically do that but today we did and when they have that many baserunners and that many chances, sooner or later something's going to happen."
Orlando Hudson hit three doubles for Arizona, which has won two of the first three games in the four-game series. Young had two hits and a walk to go with his 11th homer.
Diamondbacks starter Micah Owings (6-2) gave up six hits and three runs, two earned, in six innings. He struck out four and walked two. The Braves did not have a hit after the third inning.
Arizona added another first-inning run. Hudson hit a one-out double to left. Glavine walked Conor Jackson and Upton to load the bases, and Snyder's sacrifice fly drove in Hudson.
Johnson led off the third with a single. With two outs, Jeff Francoeur hit a liner to right that sailed over Upton's glove for a two-base error, allowing Johnson to score for a 3-2 lead.
"The game could have been different if a couple things go a different way," Johnson said. "If [Byrnes' home run] bounces off the wall a different way or doesn't go an extra inch ... it just didn't go in our favor."
Hudson's third double, off reliever Will Ohman in the eighth, drove in Young for a 7-3 lead. Young added a sacrifice fly in the ninth.
Owings, who was 4-for-5 with two homers and six RBIs in a 12-6 win at Atlanta on Aug. 18, 2007, was 0-for-3 with two strikeouts.
Braves 3B Chipper Jones was held out with back spasms. ... Atlanta C Brian McCann had a second-inning single to stretch his hitting streak to 12 games before leaving in the eighth with heat-related symptoms. Braves manager Bobby Cox said McCann should start Monday. ... Arizona 3B Augie Ojeda left in the ninth with a groin injury. Melvin said Ojeda might miss a few days but should avoid the disabled list. ... In 366 at-bats against Glavine with the bases loaded before Sunday, batters hit only .249 with one homer. Montreal's Jose Vidro hit a grand slam against Glavine and the New York Mets on Sept. 19, 2003, in New York. ... Young has two homers to lead off games this season and 11 in his career.