 The Atlanta Falcons' new defensive coordinator Mike Nolan retained Grimes and Dunta Robinson the starting cornerbacks to begin the season, ahead of Asante Samuel.He started in the Atlanta Falcons' season-opener at the Kansas City Chiefs and recorded six solo tackles before exiting in the fourth quarter of their 40–24 victory with a calf injury.On September 11, 2012, the Atlanta Falcons placed Grimes on injured reserve for the rest of the season after it was discovered he would have to undergo surgery for a torn Achilles tendon.