Sadler pushed his No. 1 JR Motorsports Chevy Camaro from 15th with 50 laps remaining for his third series victory this season and the first spot in the eight-driver second round that begins at Kansas Speedway on Oct. 15.
Ryan Blaney was third, followed by Sam Hornish Jr. and Matt Tifft.
Erik Jones, who entered the race with the championship lead, was denied a series win at Kentucky for the second time this season despite leading the 300-mile event five times for 100 laps.
Jones' chance for victory was derailed with 13 laps remaining when his No. 20 Joe Gibbs Racing Toyota was knocked out of contention after tangling with Ty Dillon's No. 3 Chevy at the exit of Turn 4.
Jones finished 28th, one spot ahead of fellow Chase contender Dillon.