Darlington in the VFW Sport Clips Help A Hero 200, beating out Denny Hamlin. The two wins would automatically lock Sadler in the inaugural Xfinity Chase. Sadler was one of three drivers starting the chase with wins. In round one, Sadler won the race at Kentucky. Sadler, with a few more top tens, moved on to the championship four at Homestead-Miami Speedway. Sadler went on to score a runner-up finish in the championship for the third time in his career. In 2017, Sadler returned to the Cup Series part-time with Tommy Baldwin Racing, driving the No. 7 in the Daytona 500. His last start in the Cup series was late in 2013. As one of the two fastest non-chartered cars in qualifying, he was able to lock himself into the race before the Can-Am Duels. He ended up qualifying for the next 2 plate races at Talladega in May and then Daytona in July and was going to drive in the Coca-Cola 600, but gave the ride to J. J. Yeley for an unknown reason. In his 800th NASCAR start at Iowa's American Ethanol E15 250, Sadler came back from the rear of the field and ended up having a great night, but was still unable to get his first win of the season. He had a great shot to win Daytona but could not, instead pushing teammate William Byron past the overtime line as a crash took place, sealing the win for Byron. Sadler clinched the first NASCAR Xfinity Series Regular Season Championship with a fifth-place finish in the Go Bowling 250 at Richmond Raceway. Sadler entered the night with a 91-point edge over JR Motorsports teammate William Byron and needed to come out of the race ahead by at least 61 points in the standings. Sadler finished the race 95 points ahead of Byron. Sadler was officially awarded the championship trophy and the 15 bonus points towards the NASCAR playoffs the following weekend at Chicagoland Speedway; the final race of the regular season. Despite not winning a single regular-season race, Sadler led the series with 11 top fives, an average finish of 9.5, and spent all but two weeks on top of the points standings. Sadler entered the playoffs as the third seed behind William Byron and Justin Allgaier and scored his 4th runner-up finish in the championship despite going winless. On February 17, 2018, he finished second