With five of 147 laps remaining, Larson had clawed his way back up to second behind Nemechek after a pit road speeding penalty left him to restart in the rear of the field at the start of the final stage.
Entering the final lap, Larson pulled alongside Nemechek exiting Turn 2 and by Turn 3 he edged ahead of Nemechek as the two collided and both hit the wall.
As both came off Turn 4 toward the start/finish line, Nemechek spun and hit the inside wall while Larson claimed the win by 1.337 seconds over Justin Allgaier.
The win is the first of the 2023 season for Larson, who was making his first start with Kaulig Racing. It’s the 14th win of his career and first in any series at Darlington.
“This feels good and it was in exciting fashion there at the end,” Larson said. “We had a really, really good car the whole race and I made a mistake and sped on pit road. We knew we’d have time to get back to the front if we got a caution.
“We were picking cars off pretty fast, got to sixth before the last round of pit stops there. The lane selections really worked out for me. I could really work that line in (Turns) 1 and 2.”
Asked to describe the final lap, Larson said, “We were able to get to (Nemechek’s) inside and just side-draft there. We were just bouncing off each other a little bit. I’m not sure what happened in (Turn) 3, but it seemed like he was trying to get in behind me to shove me in the corner.
“He kind of hooked me right and hit the wall and just tried to stay away from him off of (Turn) 4. What an exciting race there.”
Cole Custer finished third, Austin Hill fourth and Nemechek was credited with a fifth-place finish.
Completing the top-10 were Carson Hocevar, Josh Berry, Same Mayer, Kaz Grala and Corey Heim.
On newer tires, Larson powered past leader Jeremy Clements on a restart with two of 45 laps remaining and held off Nemechek by 0.446 seconds to take the Stage 1 win.
Hill was third, Custer fourth and Mayer rounded out the top five.
Both Riley Herbst and Sammy Smith were involved in early incidents on the track which knocked them out of contention for the win.
Nemechek ran down Larson on the final of 45 laps and edged him by 0.611 seconds to take the Stage 2 win.
Allgaier rallied from a pit road speeding penalty to finish third, Mayer was fourth and Custer completed the top five.
With 22 laps remaining in the stage, an 11-car wreck erupted in Turns 3 and 4 and collected several of the top contenders including Hill, Sheldon Creed, Chandler Smith, Ryan Truex, Brandon Jones and Daniel Hemric.
Following the break between Stages 2 and 3, most of the lead-lap cars elected to pit but Larson was penalized for speeding on pit road and had to restart from the rear of the field.
Hocevar, who stayed out, inherited the lead but Nemechek wasted no time powering to the lead on the restart on new tires.
With 31 laps to go, Larson had worked his way back into the top 10 but was just over 11 seconds behind leader Nemechek.
NASCAR was forced to display a caution on lap 126 for a large piece of debris on the backstretch that was hit by several cars.
All of the lead-lap cars elected to pit with Nemechek the first off pit road. When the race resumed on lap 132, Nemechek was followed by Allgaier, Custer, Hill and Larson.
Kyle Sieg wrecked off Turn 2 late in the race to set up a restart with seven laps remaining which left Nemechek the task of trying to hold off Allgaier, Hill and the fast-approaching Larson.
Larson moved in behind Nemechek with five laps remaining and began to work on him for the lead.