For 23 months straight, the Ford Mustang outsold the Chevrolet Camaro every single month — until one September, when Chevrolet edged ahead by just 148 units, 6,577 to 6,429. The swing came right as Ford halted Mustang production over a sales slide, while new 2017 Camaro ZL1s were posting 554 rear-wheel horsepower on customer dynos. Read on to see how one of America’s oldest rivalries flipped in a single month.