McDonald (4-2) didn't allow a runner to reach third base in the effort, yielding just one walk while striking out five.
The Pirates right-hander tossed 65 of his 103 pitches for strikes and lowered his ERA to 2.20 as the Bucs took the opener of a three-game series at PNC Park.
Bronson Arroyo (2-3) lasted only four innings for National League Central-leading Cincinnati, surrendering four runs on eight hits.
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