Blaney was leading all title contenders, but became agitated with Chastain as they battled for the race lead.
He did not need to win in order to be crowned champion, but felt that he needed to get out front to protect himself from the chasing Hendrick Motorsports duo of Kyle Larson and William Byron.
"He's [Chastain] backing me up to the No. 5. I have to go," the Team Penske driver explained. "He's backing me up to Larson to where I'm going to be in trouble."
As the battle became more contentious, Blaney put the bumper to Chastain. They ended up three-wide for the lead with Martin Truex Jr., and Chastain ultimately prevailed while Blaney fell back to third.
"(Expletive) right I hit him on purpose," declared Blaney. "I mean, yeah, I hit him on purpose. He blocked me on purpose 10 times. So, yeah, I hit him on purpose.
"What do you expect me to do? He's backing me up to the other championship guy, and I got to go. We were just racing hard. But do I think he was overaggressive on the blocks? Yes, very much so. Did I hit him? Yes, I did. That's just part of it."
Chastain is the first driver not part of the Championship 4 to win the finale since the elimination format's introduction in 2014.
"I was not going to crash him," he said during the winner's press conference. "I was not going to use my front bumper, side fenders, anything. Dirty air? Different story. Yeah, I'm going to. I'm going to keep the lead because that's everything.
"Before the second to last run I thought we had him covered. Coming to the end of stage two, the No. 17 [Chris Buescher] drove by me. Made some adjustments. Got too loose, we were too tight, too loose, too tight again when Blaney and the No. 19 [Truex] right there when the last caution came out. I asked [crew chief Phil Surgen] and our group to please let me turn better, make the car turn better without giving up any rear grip."
"I know he's mad and I do not care"
Chastain, always a disruptor and known for his many run-ins with fellow competitors in recent years, was unfazed by Blaney's frustration with him.
"He [Blaney] got by me one time, was not going to run him up, pinch him up. Yeah, I know he's mad and I don't care. I do not care. I did not care then. I do not care now. I'm here to race him. I'm not going to wreck him. I gave him the bottom most times. One time I was inside of him after he got by me. I crossed back over into three and I made sure to wrap the bottom. I'm not going to slide up and pinch him at all. It's in my mind the entire time, for sure."
Blaney admitted that he can get a bit too fired up on the radio, saying: "There's no secret that I can snap on the radio. That's been my whole life. That's been my whole career. It's just kind of something I do."
Chastain noted that as well, saying: "He gets angry. It's okay. I've known him for a decade. I could see him moving around in the car. The car's going straight. I could see his colorful suit and gloves. I didn't see apparently there was -- I was number one, I don't know. I could see, like, movement when I checked the camera. I was like, Oh, he is angry."
