BRISTOL, Tenn. (AP) -- Sam Mayer celebrated his recent promotion to JR Motorsports with a sweep at Bristol Motor Speedway. The teen sensation opened Thursday night with his first NASCAR national series victory with a Truck Series win and followed it immediately after with an ARCA Series win.
It was quite the party for the 17-year-old Mayer, who was hired this week to race in the Xfinity Series next season for JR Motorsports. He won in his seventh career Truck Series start -- fourth this year -- for an upset in the opening race of the playoffs.
Mayer passed title contender and teammate Brett Moffitt with 30 laps remaining to score the victory for GMS Racing. He's the second youngest Truck Series winner behind Cole Custer, who was 16 when he won at New Hampshire in 2014.
"What? Oh my gosh, Bristol, dude. I love this place," Mayer said in somewhat disbelief. "That feels so good."
Mayer had little turnaround before the ARCA event, held an hour after his Truck Series win. He completed 400 laps and the ARCA win was his fifth victory in 12 ARCA starts this year, all with GMS.
Mayer has won four consecutive races at Bristol this year in various series.
"Tonight has been awesome," Mayer said. "This coming after our JRM announcement is huge. We proved this weekend that we can do it. I love this momentum."
A win in the Truck Series by any playoff driver would have earned an automatic berth into the next round. But the field was upstaged by the teenager who signed his career-changing deal Wednesday.
Mayer first joined JR Motorsports' Late Model program in 2018, and now will return for the second half of the 2021 Xfinity Series season when he's 18 and eligible to run at that level. He is slated to race full-time in 2022.
Mayer is the son of former IndyCar and road racing driver Scott Mayer. He's run a mixed schedule this year of ARCA, and ARCA East and West series races, winning eight times.
Moffitt led a race-high 117 laps, finished second and moved to the top of the Truck Series standings. The defending race winner made it a 1-2 finish for GMS Racing. Sheldon Creed and Zane Smith, both GMS drivers also in the playoffs, finished 12th and 17th.
"I am proud of everyone at GMS for bringing not just mine, but Sam's and Sheldon and Zane all having fast trucks in the playoffs," Moffitt said. "That's what we need. We need to have four trucks at Phoenix racing for a championship and this is a good start."
Tanner Gray was third and followed by Parker Kligerman, Chandler Smith and Grant Enfinger sixth -- the second best finish among playoff drivers. Trevor Bayne initially finished fifth but was disqualified for failing post-race inspection.
Tyler Ankrum picked up his first career stage victory and finished seventh, followed by Ross Chastain and Johnny Sauter.
Moffitt has a 37-point lead over eighth-place, the cutoff line, for the playoffs. The series goes to Las Vegas Motor Speedway next week then eliminated two drivers at Talladega Superspeedway in October. Christian Eckes and Todd Gilliland are both below the cutline.