McDonald (2-2) yielded two hits and four walks while striking out nine en route to the victory, the Pirates' second straight over the Braves.
Andrew McCutchen's one-out RBI double off the right-field wall in the sixth erased a 1-0 Pirates deficit and Sanchez followed with a two-run shot to center for the decisive blow.
Braves starter Paul Maholm (3-1), after starting the season with 25 2/3 scoreless innings, was reached for the three runs on four hits over six full frames.
Andrelton Simmons provided Atlanta's only RBI.
NBC reportedly holds celebs hostage to Jimmy Fallon's show
Boston schools pull out free condoms over wrapping complaints