SPARTA, Ky. — Driving his backup car, Brad Keselowski raced to third win of the year, grabbing the lead with 55 laps remaining and holding off all challengers Saturday night in the NASCAR Sprint Cup race at Kentucky Speedway. The 28-year-old from Rochester Hills, Mich., picked up his seventh win in his five years on the circuit. He won earlier this year at Bristol and Talladega.