Peterson was optioned to Triple-A Syracuse after the first game of Saturday's doubleheader, Anthony DiComo of MLB.com reports.
The left-hander was excellent in the matinee, striking out five and holding Atlanta to three hits and three walks over 5.1 scoreless innings in a Mets victory to improve to 6-2 on the season. Peterson will likely be back with the Mets when they require a temporary sixth starter for their Aug. 20 doubleheader with the Phillies.