Matt Carpenter drove in a pair of runs as the NL Central champion Cardinals kept winning after a 3-3 start.
Zack Cozart homered for the Reds, who have lost three in a row and six of seven. Cincinnati speedster Billy Hamilton left in the eighth inning after beating out an infield single.
Martinez (1-0) gave up one run on three hits, striking out four and walking two.
Trevor Rosenthal picked up his fourth save in as many opportunities. He struck out Joey Votto with two on to end the game.
Homer Bailey (0-1) surrendered five runs and nine hits over 5 2-3 innings. He made his first start after beginning the season on the disabled list while recovering from surgery on a torn flexor tendon.
