Giants starting pitcher Trevor McDonald suffered the loss after surrendering three runs and seven hits over 5 1/3 innings of work.
San Francisco dropped to a 33-48 record at the official midway point of their season, marking their fewest victories through 81 games since 2017.
The Giants offense finished 0-for-8 with runners in scoring position and committed two defensive errors, bringing their season total to 56 errors.
Rafael Devers drove in the lone run for San Francisco with an RBI double in the first inning, while rookie catcher Drew Cavanaugh singled in his major league debut after being elevated from Triple-A Sacramento.
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The weekend series continues at Oracle Park on Saturday night with Braves right-hander Bryce Elder scheduled to face Giants ace Logan Webb.
