The Reds, who had a five-game winning streak snapped Thursday, bounced back with an escape-filled pitching performance from Bronson Arroyo and a big inning that featured five extra base hits.
With Travis Wood on the mound and the Cubs leading 2-1, Ludwick tied the contest by hitting the first pitch of the fourth over the wall in left-center. After Jay Bruce was hit by a pitch, Frazier put the Reds in front for good a two-run blast.
Two outs later Arroyo helped his own cause with a double and then scored on a double by Zack Cozart. A triple by Drew Stubbs brought home the fifth and final run of the inning.
Arroyo (9-7) gave up nine hits but only three runs over 6 1/3 innings to get the win. All of the Cincinnati runs came off Wood (4-9), who left after five innings.
Cincinnati has produced a 21-7 record since July 18 to take command in the National League Central pennant race.