The Braves’ biggest late-season series in five years got off to a good start Thursday night at SunTrust Park.

The Braves broke a 3-3 tie in the seventh inning on back-to-back doubles by Dansby Swanson and pinch-hitter Lucas Duda, added four runs in the eighth inning and defeated the Philadelphia Phillies 8-3 in a meeting of the top two teams in the National League East.

The win extended the first-place Braves’ lead to a commanding 6-1/2 games over the second-place Phillies with nine games to play and trimmed Atlanta’s magic number to four.

The series continues Friday night, Saturday afternoon and Sunday afternoon.

If the Braves win two of the next three games, they will clinch their first division title since 2013.

“It’s fun. Obviously these games mean a lot, and as a player that’s all you can ask for -- to be in September playing meaningful games,” said Kevin Gausman, who worked into the seventh inning as the Braves’ starting pitcher Thursday. “Coming from Baltimore (in a July 31 trade) with the season we were having there, the playoffs were kind of a far-fetched dream. So to be in this situation,  it’s great.”

Several hours before Thursday’s game, Swanson was asked what type of atmosphere he expected in this series.

“I just expect a lot of energy, both on the field and in the stands,” he said.

He demonstrated such energy by leading off the seventh inning with a hustle double to left field.

“He’s always looking to go to the next base,” Braves manager Brian Snitker said. “I mean, how many times have we seen him do that this summer? He’s got a good feel and a good instinct for that.”

Swanson scored the go-ahead run when the next batter, Duda, doubled to right field.

Swanson had two hits for the night after entering the game with just just six hits in his past 43 at-bats. But he also entered the game hitting .316 in the seventh inning or later this season.

The Braves’ eighth-inning insurance runs came on a bases-loaded walk by Swanson, sacrifice flies by pinch-hitter Charlie Culberson and Ronald Acuna and an RBI single by Ender Inciate. Swanson stole second base with two out in the inning and scored the final run on Inciarte’s hit.

Gausman, who allowed five hits and two walks in the first three innings, retired the Phillies in order in the next three innings to stabilize the game for the Braves. He retired the last 11 batters he faced before yielding to the bullpen with one out in the seventh and the game tied 3-3.

“They kind of got to me early, but I just kind of reined it in,” Gausman said.

The Braves’ bullpen  worked the final 2 2/3 innings, allowing one hit and no runs. Jesse Biddle got the last two outs of the seventh. Arodys Vizcaino worked a 1-2-3 eighth, a promising development for the Braves. Chad Sobotka struck out the side in the ninth.

The Phillies used eight pitchers in the game.

In the early innings, both teams were hurt by familiar nemeses -- the Braves by their pitchers walking batters and the Phillies by their poor defense.

The Braves have walked more batters than any other National League team this season, and that tendency surfaced when the Phillies’ second batter of the game, Rhys Hoskins, drew a walk off Gausman. Hoskins scored to give the Phillies a 1-0 lead.

The Braves took a 2-1 lead in the bottom of the first inning with help from the Phillies’ defense, which ranks last in the major leagues in defensive runs saved. Although the Phillies weren’t charged with an error, two infield misplays helped the Braves score two runs.

The Phillies answered with two runs in the third inning for a 3-2 lead, with one of the runners who scored having reached base via a leadoff walk by Gausman. But a sacrifice fly by Johan Camargo tied the game in the bottom of the third, and that 3-3 score held until the Braves’ characteristic late-game rallies decided the opening game of this NL East showdown series.

"It's always huge to get the first one of a series, no matter who you are playing," Braves catcher Kurt Suzuki said. "Take it today and then carry the momentum over tomorrow."