He also got some help from Elliott Sadler, who had a rough day start to finish.
The two title contenders started Saturday tied for the championship, and likely would have gone into next weekend's finale at Homestead-Miami Speedway locked into a tight race. But as Stenhouse battled Joey Logano and Brian Vickers for the lead headed to the white flag, Elliott Sadler imploded 10 positions behind them.
Sadler was racing hard for 12th with Justin Allgaier and Cole Whitt when he triggered a three-car accident.
"I just got loose. It's hard to put this into words," Sadler said. "It's been a long, great season and my guys deserve better effort from me than wrecking the car on the last lap."
The accident brought the race to a halt, and Sadler had to sit in his battered car as NASCAR cleaned the track.
Once cleared, he returned to pit road for some futile repairs, but the race went on without him into overtime.
Logano pulled away in his Joe Gibbs Racing Toyota for his ninth win of the season, with Vickers finishing second.
Stenhouse wound up third, and Sadler, his wounded car sputtering and sparking, was 22nd.
Sadler was 10 points behind Stenhouse before the accident, but now goes to the finale down by 20. It capped a day that saw him wreck his primary Chevrolet on his qualifying lap, and it took his Richard Childress Racing team almost until the start of the race to get his backup car prepared.
"I did it to myself. I put my team in a hole, qualifying like we did," he said. "We tried to work on this car as much as we could, and I just got a little loose there and got into (Whitt). It was 100 percent my fault. I should have done a better job for these guys and I just apologize to them for putting them in this position heading into Homestead. We don't have a dog in the fight, but I definitely dug ourselves a hole."
Stenhouse needs to finish 16th or better at Homestead to become the sixth driver in Nationwide history to win consecutive titles.
"That makes us feel good, but we've given up 20 points in one race, so it's not over 'til it's over," he said. "We've still got some work to do, but it feels pretty good."
Stenhouse also said it will be difficult putting a strategy together with his Roush Fenway Racing team for next week.
"It's going to be tough because I'm going to have to not push the limits as much as I like," he said. "I like going for race wins, too, so it's going to be a fine balance there because I want to win that race and win the championship all at the same time. We were close last year running second there at the end and finished second, and kind of had to share the burnout stage there with (race winner) Brad (Keselowski), so hopefully we don't have to do that."