Brian McCann’s first-inning homer off Brian Matusz (5-7) gave Atlanta a 1-0 lead. The Orioles scored two runs off Tommy Hanson in the fourth with help from a throwing error by Simmons at shortstop and a fielding error by Michael Bourn in center field.
Chad Durbin (3-0) struck out the two batters he faced after taking over for Hanson in the sixth.
The Braves snapped a four-game losing streak.
Matusz fell to 0-6 in seven career interleague starts. He gave up four runs, nine hits and three walks in 5 2-3 innings.
The Orioles began the night one-half game behind the first-place Yankees in the AL East. New York beat Washington 7-2.
Simmons had three hits.
Kris Medlen, recalled from Triple-A Gwinnett before the game, gave up one hit and one walk in two scoreless innings to set up closer Craig Kimbrel, who pitched the ninth for his 19th save.
The Orioles hit into four double plays to boost their total to 72, the most in the major leagues. Matt Wieters’ grounder to Simmons with the bases loaded in the third started an inning-ending double play. Pinch-hitter Nick Johnson hit into a double play to end the game.
Hanson showed his frequent disagreement with home plate umpire Derryl Cousins’ strike zone as he set a career-high with six walks in 5 1-3 innings.
Hanson gave up four hits and two unearned runs. He was pulled after consecutive walks in the sixth. He took a look at Cousins as he walked off the field.
The Braves made several strong defensive plays in the game, but the defense let Hanson down with two errors in the fourth. Simmons threw high to first after fielding Mark Reynolds’ grounder.
Reynolds scored as Bourn bobbled Wilson Betemit’s double in center, allowing Reynolds to score from first and Betemit to advance to third. It also was Bourn’s first error.
Betemit scored, barely beating right fielder Jason Heyward’s throw to the plate, on Steve Pearce’s fly ball. Betemit, who began his career with the Braves, had two hits.
Simmons’ homer, which landed in the first row of the stands in left, drove in Matt Diaz, who singled, to give Atlanta a 3-2 lead. It was the second homer for Simmons, who made his debut on June 2.
Pinch-hitter Jack Wilson followed with a triple to center and he scored on Bourn’s soft single up the middle.
Chris Davis, normally a first baseman or designated hitter, made his first career start in right field for Baltimore. He made a tumbling catch near the foul line on Chipper Jones’ sinking liner in the sixth.
With Freddie Freeman still bothered by a sore left index finger and thumb, Atlanta’s Martin Prado made his first start of the season at first base.
Prado delivered with a strong play in the first inning as he snagged a grounder by Davis and threw to Simmons to start a double play. Dan Uggla opened the game with a strong play at second base, diving to his left to stop a grounder by Brian Roberts before completing the play with the throw to first.
Prado made another strong play to end the seventh as he made a leaping stab of another sharply hit grounder by Davis.
Bourn, charging toward the infield, made a diving catch of J.J. Hardy’s shallow fly ball in the fifth.
NOTES: The Braves designated RHP Livan Hernandez for assignment. Hernandez, 37, gave up seven hits and five runs in 1 2-3 innings against Toronto on Sunday. He was 1-1 with a 4.94 ERA and one save. ... Orioles OF Nolan Reimold, who has been on the DL since May 4 with a herniated disc in his neck, will see a neurosurgeon in Baltimore. Manager Buck Showalter said he expects a report Monday. .... Hanson’s strikeout of Wieters in the sixth was the 500th of his career. ... Brandon Beachy, who leads the majors with a 1.98 ERA, will face Baltimore’s Jason Hammel on Saturday night.