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.
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