Lowe (6-2) allowed two runs and five hits in 7 1/3 innings to move into a tie for the NL lead in wins. He has allowed two runs or less in seven of his 10 starts.
Lyle Overbay's RBI single off Mike Gonzalez cut Atlanta's lead to 4-3 in the ninth. Rod Barajas then walked to load the bases but Soriano struck out pinch-hitter Kevin Millar and retired Marco Scutaro on a flyball to left to earn his fourth save.
"Soriano came in and did an unbelievable job," Lowe said. "I think that's the benefit of having two guys who are comfortable closing. Clearly Gonzalez is our closer. But when the situation come about it's very comforting to everybody to see a guy come in like that. Because you see now he's very comfortable in that role."
Gonzalez earned his seventh save in Friday night's 1-0 win over Toronto but left the tying run on third base.
Kelly Johnson hit a seventh-inning homer off B.J. Ryan as the Braves (22-20) moved two games over .500 for the first time since April 15, when they were 5-3.
The Braves have won 11 of 16 and are 5-3 on their nine-game homestand. They began the stretch at Turner Field with the worst home record in the majors.
"We needed to starting playing better at home, I think that's the most important thing," Lowe said.
"It starts with starting pitching. You've got to be able to keep your team in the game. I think that's what we've been able to do."
The AL East-leading Blue Jays have lost five straight, all on the road. It's their longest streak since losing seven straight from June 14-21, 2008.
"We haven't shown up so far in this series," manager Cito Gaston said. "These guys have got to start swinging their bats like they did before this road trip. ... You have long streaks like this. You just have to keep going."
Lowe, who entered with a .143 batting average, was 2 for 3, including a fourth-inning single that drove in Jeff Francoeur for a 3-2 lead. Francoeur had three hits.
Toronto right-hander Casey Janssen (0-1) gave up three runs and eight hits over six innings in his first start since 2006 and his first appearance since 2007. Janssen missed last season recovering from a torn labrum.
"I could have made some better pitches," Janssen said. "I'm back. That was my goal."
Scutaro gave Toronto a 2-0 lead with a two-run double in the third.
With light rain beginning to fall in the bottom of the fourth, Francoeur hit a one-out double and Diory Hernandez walked. After the runners advanced on Jordan Schafer's grounder, Lowe's single to right drove in Francoeur.
Hernandez was a late addition to the lineup after shortstop Yunel Escobar was scratched with a strained right hip flexor. Hernandez made his first career start.
There was rain, but no delay, over the last six innings.
- Atlanta 3B Chipper Jones was held out for the second straight game with a sore right big toe. He said he hopes to play Sunday.
- Escobar is listed as day to day.
- Lowe reached 2,000 career innings in the fifth.
- Janssen's previous start was on July 24, 2006, for Toronto at Seattle, when he gave up six runs in three innings.
- Braves LHP Tom Glavine (sore left shoulder) gave up three runs and five hits over three innings in his rehab start for Triple-A Gwinnett against Toledo on Saturday night.