The Cardinals had lost the previous 10 games started by Montgomery (3-7). He stopped that streak by striking out six and allowing just three hits
Giovanny Gallegos got the final four outs to earn his eighth save.
Nolan Arenado, Jordan Walker and Nolan Gorman hit two-run homers as the Cardinals won their second straight game
Reds starting pitcher Ben Lively (3-4) allowed seven runs on 10 hits in 6 2/3 innings. He struck out eight
Stuart Fairchild drove in two runs for the Reds, who lost their second straight game
The Cardinals moved ahead 2-0 in the first inning when Brendan Donovan hit a leadoff single and Arenado hit his homer two outs later
St. Louis doubled its lead to 4-0 in the bottom of the inning when Paul DeJong hit a single and Walker launched his two-run homer.
The Cardinals pushed their lead to 5-0 with two outs in the fourth inning. Walker hit a single, Dylan Carlson walked and Donovan hit an RBI single
The Reds broke through in the seventh inning off Jordan Hicks. Spencer Steer led off with a single, Tyler Stephenson walked and Fairchild hit an RBI single
Will Benson drew a one-out walk to load the bases. Kevin Newman greeted Andre Pallante with a sacrifice fly to cut the lead to 5-2, but Willson Contreras ended the rally by nailing Benson trying to steal second base.
The Cardinals restored their five-run lead in the bottom of the inning on Donovan's bunt single and Gorman's two-run blast
Cincinnati cut its deficit to 7-4 in the eighth inning. Chris Stratton walked Matt McClain, allowed Elly De La Cruz's infield single and walked Steer to load the bases.
Stephenson hit a sacrifice fly and Fairchild hit an RBI double. But Gallegos relieved Stratton and retired TJ Hopkins on a groundout to end the rally.
--Field Level Media