Nemechek and Joe Gibbs Racing teammate Chandler Smith battled back-and-forth for the lead much of the race but it was Nemechek who was out front at the start of the final round of green flag pit stops late in the final stage.
Once all the cars cycled through their stops, Nemechek emerged with a more than five-second lead and eventually took the checkered flag by 4.360 seconds over Cole Custer as Smith settled for third.
Although Smith won the first two stages, Nemechek led the most laps (99 of 200).
Watch: John Hunter Nemechek: ‘It’s awesome to come back and win’ in Xfinity Series
“Hats off to all the guys on this No. 20 team for Joe Gibbs Racing. Man, it’s awesome to come back out here and win in the NASCAR Xfinity Series,” said Nemechek, who competes full-time in Cup with Legacy Motor Club. “It feels so good to win here in Las Vegas.”
Nemechek’s win halted Hill’s two-race winning streak to open the season and Nemechek became the first non-Chevrolet driver to win a NASCAR national series race through the first eight events.
Hill ended up fourth and Riley Herbst rounded out the top five.
Completing the top 10 were A.J. Allmendinger, Ryan Sieg, Sammy Smith, Brandon Jones and Justin Allgaier.
Stage 1
Chandler Smith led all 45 laps on his way to a dominating Stage 1 win over Nemechek. Hill ended up third, Herbst fourth and Custer rounded out the top five.
Three-time Supercars champion Shane van Gisbergen was forced to retire early from the race after he developed engine issues in his No. 97 Chevrolet. He completed just 27 laps.
Stage 2
Chandler Smith used a last lap pass through Turns 3 and 4 to get around Nemechek and claim the Stage 2 win in dramatic fashion. Herbst was third, Allgaier fourth and Allmendinger fifth.
Stage 3
During the break between Stages 2 and 3, all the lead lap cars pit with Chandler Smith first off pit road. When the race resumed on lap 97, Smith led Herbst and Nemechek.
A caution for the stalled car of Parker Retzlaff on lap 124 sent all teams down pit road for new tires and fuel with Nemechek the first off. He led Chandler Smith and Hill on the restart with 72 laps remaining.
With 50 laps to go, Nemechek remained in command with a 1.2-second lead over Herbst and Chandler Smith in third.
Chandler Smith was among the first to hit pit road and kick off the final round of green flag pit stops with 34 laps remaining.
Jeb Burton was caught speeding on pit road during his stop and was forced to serve a pass-through penalty. Burton refused at first to bring his car to pit road within three laps and NASCAR briefly stopped scoring the car.
Once the cycle of stops was completed, Nemechek returned to the lead with 10 laps to go.