Gio Gonzalez had been the scheduled starting pitcher in Wednesday night's game. Instead, Treinen is making his sixth start of the year.
Treinen is 2-3 with a 2.18 ERA in 13 games. His last start came on June 28, when he allowed two runs in five innings in a 7-2 win at the Cubs.
Washington manager Matt Williams also made some lineup adjustments. Michael Taylor is starting in center field and batting leadoff. Tyler Moore is playing first base and hitting cleanup. Left fielder Steven Souza, third baseman Kevin Frandsen, second baseman Jeff Kobernus and catcher Sandy Leon also are starting against the Braves.