The 29-year-old Chastain from Alva, Florida, rallied from an early pit road speeding penalty to overtake Erik Jones on the final lap through the tri-oval to claim his second career win in NASCAR's premier series.
The two-time Cup champion from Las Vegas, Nevada, benefitted from a final lap collision involving Tyler Reddick and Chase Briscoe to become the ninth different competitor to reach 60 victories in NASCAR's premier series.
The Tucson, Arizona, native made a late two-tire pit strategy work to his advantage after fending off teammate Larson in overtime to capture first victory at Vegas.
The reigning NASCAR Cup Series champion led four times for 28 of 200 laps and fended off the field in a four-lap shootout to claim his second victory at Auto Club Speedway.
