Beating Washington for the 18th time in the last 25 series matchups, Atlanta is hoping to use another fast start against the Nationals to win a second straight NL East title.
The Braves have won five of six against the Nationals this year.
Washington began the day by placing third baseman Ryan Zimmerman placed on the 15-day disabled list with a broken right thumb.
Gonzalez (2-1) continued his struggles against the Braves, giving up nine hits, six runs and four walks and striking out six in six innings.
Despite ranking second in the majors among left-handers with 34 wins since the start of 2012, Gonzalez is 2-7 with a 5.31 ERA in 10 starts against the Braves during that span.
He hasn't received more than one run of support in any of his last seven winless starts against Atlanta.
Harang, making his 322nd career and third with the Braves, improved to 2-4 with a 3.72 ERA in 10 starts against Washington.
Ross Detwiler faced the minimum in the seventh for the Nationals, but he gave up four unearned runs in the eighth on Freeman's RBI double and Andrelton Simmons' first homer, a three-run shot that put the Braves up 10-1.
Gonzalez's struggles began in the first.
After walking leadoff hitter Jason Heyward, Gonzalez made an errant underhanded throw to first baseman LaRoche on B.J. Upton's bunt single. The ball rolled away from LaRoche, allowing Heyward to advance to third and B.J. Upton to second.
Freeman's sacrifice fly scored Heyward, and Justin Upton homered to make it 3-0.
Atlanta added three more runs in the second.
Tyler Pastornicky led off with a triple and scored on Heyward's RBI double. Freeman followed with his fourth homer to give the Braves a 6-0 lead.
Gonzalez stranded two runners when Justin Upton struck out in the fourth and stranded the bases loaded in the fifth when Heyward popped up.
NOTES: Washington RF Jayson Werth returned after a sore groin forced him from the lineup on Saturday. Werth went 0 for 4 with two strikeouts and stranded three runners. ... Simmons hit in the No. 5 spot for the first time in his career, going 2 for 5 with three RBIs. ... Washington LF Steven Souza Jr. made his major league debut in the seventh as Frandsen moved to second base and Danny Espinosa left the game. Souza struck out in the eighth. ... The Nationals called up INF Zach Walters from Triple-A Syracuse to take Zimmerman's spot on the 25-man roster. Walters struck out as a pinch-hitter to end the game. ... Span, on the seven-day DL with concussion symptoms, missed his second straight game.