Busch lined up fourth heading into the second overtime of Saturday night’s race at Kansas Speedway and had struggled on the previous overtime restart.
Chastain led the way with Austin Hill quickly giving chase but Chastain developed a bad tire-rub and Busch went to the outside and passed both Chastain and Hill exiting Turn 4 with one lap remaining.
He held off them both to claim his second series win of the season and 61st of his career. Busch has not finished worse than second in his four Truck starts this season.
The win was also the fifth in a row for Kyle Busch Motorsports, tying a series record.
“No restarts went our way tonight. We definitely missed something, coming up through the gears it just would not go,” Busch said. “It was just slow and those guys would just swarm us.
“All in all, a great job by KBM.”
Christian Eckes finished fourth and John Hunter Nemechek rounded out the top-five.
Completing the top-10 were Todd Gilliland, Zane Smith, Raphael Lessard, Johnny Sauter and Ben Rhodes.
Following the break between Stages 2 and 3, the lead-lap trucks all pit with Nemechek the first off pit road.
On the restart on Lap 68, Nemechek was followed by Busch, Sheldon Creed, Zane Smith and Stewart Friesen.
Busch went three-wide on the inside on Lap 69 to reclaim the lead. One lap later, Carson Hocevar spun off Turn 2 after contact with Eckes to bring out a caution.
The race returned to green on Lap 75 with Busch still leading the way.
A four-truck battle for the lead erupted after the restart with Creed returning to the race lead.
With 40 laps remaining, Creed held a small advantage over Nemechek but Busch was closing in on both.
Several drivers began a round of green-flag pit stops on Lap 37 to take on new tires and fuel to make it to the finish of the race.
Tanner Gray was penalized for speeding and had to serve a drive-thru penalty down pit road.
Once the cycle of stops was completed on Lap 119, Busch emerged as the leader after passing Nemechek on Lap 115. Nemechek had exited pit road with the lead originally.
On Lap 118, Creed hit the wall and was forced to pit under green for repairs, knocking him out of contention for the win.
With 10 laps to go, Busch held nearly a 1-second lead over Nemechek with Chastain running in third, more than 8 seconds behind the leader.
On Lap 129, NASCAR displayed a caution for the stalled truck of Jennifer Jo Cobb, who was stuck at the end of pit road.
Most of the lead-lap trucks remained on the track, including Busch, but Nemechek was among those who pit for tires, although he did not have a new set remaining.
On the restart heading into overtime, Busch led the way followed by Chastain, Rhodes, Zane Smith and Friesen. Nemechek lined up 11th on the restart.
Busch did not get a good restart and Friesen wrecked on the backstretch after getting hit by Derek Kraus, which brought the caution back out immediately.
The race went into a second overtime with Chastain in the lead followed by Zane Smith, Bayley Currey, Busch and Austin Hill.
Busch completed a sweep of both stage victories, cruising to a more than 3-second win over Nemechek.
Creed was third, Austin Hill fourth and Zane Smith rounded out the top-five.
Following the break between Stages 1 and 2, all the lead-lap trucks elected to pit with Busch the first off pit road.
On the restart on Lap 38, Busch was followed by Creed, Nemechek, Austin Hill and Gilliland.
Creed muscled his way around Busch on the restart to reclaim the lead. Busch battled back to return to the top spot on Lap 40.
With 15 laps to go in the second stage, Busch maintained a small lead over Creed while Austin Hill ran third.
On Lap 51, Hailee Deegan moved into the top-10 for the first time while Busch expanded his lead to more than a second over Creed.
With five laps remaining, Busch remained out front, more than 3 seconds ahead of Nemechek, who moved into the second spot.
Busch grabbed the lead with five laps remaining and held off Nemechek to take the Stage 1 win.
Creed was third, Rhodes was fourth and Matt Crafton rounded out the top-five.
Nemechek, who started on the pole and led the first 11 laps until Creed got around him to move into the top spot on Lap 12.
With 10 laps to go in the first stage, Creed maintained a small but stead advantage over Nemechek as Busch ran third.
With five laps remaining, Busch got around Nemechek, who had to save his truck from spinning out, to move into the second spot behind Creed.
On Lap 26, Busch ran down Creed to take the lead for the first time in the race.