Cueto (11-5) stymied the Diamondbacks on four hits, overcoming four walks while striking out three for the Reds, who came into the contest with a one-game lead over second-place Pittsburgh in the National League Central.
Ludwick's clout in the third inning extended the Reds' one-run lead and Cincinnati went to on even the four-game series at one victory apiece.
Arizona's Trevor Bauer (1-2) allowed only one hit -- Ludwick's homer -- but surrendered five walks in his three-inning stint, yielding four runs (three earned) overall.
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