Keselowski raced into the lead just before a multi-car crash triggered by Jamie McMurray ended the contest under caution.
McMurray broke away from a last-lap duel with Kevin Harvick but was caught up in a crash that engulfed Dennis Setzer's car in flames. No one was hurt in the accident, which allowed Keselowski to win a Nationwide race at Talladega for the first time.
Harvick was attempting to win his second race of the day after capturing the Talladega Sprint Cup Series event earlier Sunday. In that race, he passed McMurray just before the start-finish line and bested him by inches for the win.
The Aaron's 312 had been postponed from Saturday following heavy rain and tornado warnings in Alabama.