Forsythe homered in his first at-bat of the season, Venable added a three-run homer and Jason Marquis won his seventh straight decision to lead the Padres to a 7-6 victory against the Braves on Monday night.
"Two runs through eight, I'll take that tomorrow," manager Bud Black said. "The ninth inning got away from us a little bit, but we had a big enough cushion. The end result is what you look for."
Braves rookie Evan Gattis had a pinch-hit, three-run homer with one out in the ninth off Tim Stauffer to pull the Braves to 7-5. Dan Uggla and Chris Johnson were aboard on singles for Gattis' 14th homer overall and his fourth pinch-hit shot. He leads all major league rookies with 14 homers and 37 RBIs.
Heyward homered to straightaway center field with two outs in the ninth, his second solo shot of the game and fifth of the season. It came off Dale Thayer, who got the final two outs for his first save in three chances.
Marquis (8-2) held Atlanta to two runs and five hits, walked five, and struck out four.
"He pitched well. He weaves his way through a game. It's great," Black said.
Marquis has won seven straight decisions over nine starts, the second-longest streak of his career. His last loss was April 22 to Milwaukee.
"I just tried to carry over what I did in L.A. and try to be real consistent in my delivery and focus down in the zone with my sinker," said Marquis, who beat the Dodgers 6-2 while allowing only three hits in 6 1/3 innings in his previous start. "It helped me get deep into the game."
Marquis said keeping the ball down "is a key for me against any team. By no means am I overpowering, so I pitch to contact and my contact has to be on the ground. If I keep the ball in the bottom of the zone, I'm going to get those consistent ground balls."
Heyward homered on a slider from Marquis.
"Probably bad pitch selection, but at that point of the game, up 7-1, sometimes I like to try different things to see where it gets me," Marquis said. "I should have attacked him with a sinker like I'd been doing all night, but he put a good swing on it. He'll do some damage with mistake pitches."
The Braves lost for just the third time in 10 games.
"I'm really, really proud of this team," Heyward said. "We have a good team. We don't quit. We have a lot of fun and have a lot of pride, and that's an example of it right there."
Seeing a four-run ninth inning "is the bright side of the game," manager Fredi Gonzalez said. "You start seeing guys like Heyward and B.J. (Upton) and Justin (Upton) swinging the bats. And Gattis with his fourth pinch-hit home run. You just keep running him out when you get the situation. His swing works. He's got a short swing and he's a big, strong man."
Both of San Diego's homers came off rookie Julio Teheran, who had a no-hitter through 7 2/3 innings in his previous start.
Forsythe was reinstated from the 60-day disabled list earlier in the day to take the spot of rookie Jedd Gyorko, who was put on the 15-day DL with a strained groin.
Forsythe hit a two-out shot to left-center in the second, estimated at 445 feet.
Teheran (4-3) went six innings, allowing five runs and six hits with three strikeouts and no walks.
The Padres added two runs in the seventh on Yasmani Grandal's single and Marquis' double-play ball.
To make room for Forsythe on the 40-man roster, the Padres designated C John Baker for assignment. ... Gyorko is hitting .284 with eight home runs and 25 RBIs. He has made 51 starts at second base and nine at third. He leads all rookies in batting average, hits (66), runs (36) and total bases (107) while being tied for the lead in doubles (17) and second in home runs and RBIs. Gyorko was hurt in a loss Sunday at Colorado. ... Forsythe was placed on the 15-day DL before the season with plantar fasciitis in his right foot. He was transferred to the 60-day DL on April 24. ... Padres closer Huston Street pitched a simulated game Monday. Street will pitch an inning Wednesday at Class A Lake Elsinore. Street went on the 15-day DL on June 1, retroactive to May 30, with a strained right calf. Manager Bud Black said Street threw well Monday.