Smith went three-wide with then-leader Sheldon Creed and Kyle Busch Motorsports teammate John Hunter Nemechek following a restart with five of 200 laps remaining.
Nemechek was first to clear to the lead but as he came off Turn 4, he veered to the right and Smith went inside and claimed the lead for the first time in the race.
From there, Smith held off Grant Enfinger by .422 seconds to win Thursday night’s race at Bristol (Tenn.) Motor Speedway. Not only was it his first career victory but facing elimination from title contention, Smith’s win automatically locked him into Round 2.
“Man, God is good. God is so damn good,” Smith, 19, said. “I’ve really been tested here the last year or two and tested my faith. I have to thank everyone behind me. This is just incredible. I’m speechless right now.
“I feel like Truck races are the hardest out of all three series right now. In 2019 I felt like I was really, really good. Nothing has changed about me – the competition has gotten a lot harder.
“It’s just finally paid off.”
Todd Gilliland and Austin Hill were eliminated from further title contention. Also advancing to the second round are Creed, Nemechek, Matt Crafton, Stewart Friesen, Carson Hocevar, Zane Smith and Ben Rhodes.
Nemechek ended up third in the race, Friesen fourth and Johnny Sauter fifth.
Creed, who led 189 laps, suffered a flat tire on the final restart and ended up 19th and two laps down.
Following the break between Stages 2 and 3, most of the lead-lap trucks elected to pit with Creed the first off pit road.
Austin Hill and Tyler Ankrum were penalized for speeding on pit road and Zane Smith was penalized for his team throwing equipment. All had to restart the race from the rear of the field.
When the race resumed on Lap 122, Hocevar – who stayed out – led the way. He was followed by Creed, Friesen, Enfinger and Nemechek.
Creed quickly powered back into the lead entering Turn 3 after the restart.
Hailie Deegan spun Parker Kligerman on Lap 130 in an incident that also collected Clay Greenfield to bring out the seventh caution of the race.
The race resumed on Lap 137 with Creed out front followed by Hocevar, Enfinger and Nemechek.
Taylor Gray, Zane Smith, Chase Purdy and Jennifer Jo Cobb wrecked off Turn 4 on Lap 155 to bring out a caution.
The race returned to green on Lap 164 with Creed out front followed by Hocevar, Nemechek and Enfinger.
Nemechek quickly moved into second on the restart behind Creed.
Kligerman spun off Turn 2 with a flat tire on Lap 172 to bring out the ninth caution of the race. The leaders stayed on the track and Creed remained out front on the restart on Lap 178.
Austin Wayne Self spun off Turn 2 on Lap 180 to put the race back under caution. Creed continued to lead the way when the race returned to green with 14 laps to go.
On Lap 189, a multi-truck wreck erupted between Turns 1 and 2 as Austin Hill got loose, hit the end of the pit road wall and collected Deegan, Self, Derek Kraus, Lawless Alan and Josh Berry.
The race was halted for nearly eight minutes as the track was cleared of debris. When the race returned to green with five laps to go, Creed was followed by Chandler Smith, Nemechek and Hocevar.
Creed completed a sweep the stage wins, besting Ankrum by 3.1 seconds to take the Stage 2 victory.
Austin Hill was third, Zane Smith fourth and Chandler Smith rounded out the top-five.
Following the break between Stages 1 and 2, a handful of lead-lap trucks pit but Creed remained on the track and in the lead when the race returned to green on Lap 67.
On Lap 70, Drew Dollar got loose and hit the wall coming off Turn 2. He drifted across the track and triggered a multi-truck incident that collected Danny Bohn, Howie Disavino III, Tate Fogleman, Dawson Cram and Spencer Boyd.
The race was red-flagged for nearly seven minutes to clean fluid and debris from the track. Creed remained in the lead when the race returned to green on Lap 80.
With 20 laps remaining in the stage, Creed led Austin Hill by 1.7 seconds as Ankrum ran third and Chandler Smith fourth.
Creed held off Austin Hill on a one-lap dash to take the Stage 1 win.
Crafton was third, Zane Smith fourth and Enfinger rounded out the top-five.
Creed started on the pole and took the lead early before a caution was displayed on Lap 3 after Sam Mayer wrecked off Turn 2.
The race returned to green on Lap 14 with Creed out front followed by Nemechek and Crafton.
On Lap 22, Tanner Gray wrecked off Turn 2 to bring out another caution. The race returned to green on Lap 33 with Creed still in command.
With 10 laps remaining in the first stage, Creed has built a 3.8-second lead over Crafton while Austin Hill ran third.
Spencer Boyd spun on Lap 49 after contact with Disavino to bring out another caution. Several lead-lap trucks elected to pit but Creed remained on the track and in the lead on the restart with one lap to go.