Byron has more wins than any other driver in the NASCAR Cup Series this year, but narrowly escaped elimination as his 30-point buffer evaporated during the race.
The Hendrick Motorsports Chevrolet driver was mired in the midpack for most of the race and ended up finishing 13th, one lap down, but it proved was just enough as Byron advanced by just eight points over Denny Hamlin.
Byron will face Martinsville winner Ryan Blaney (Team Penske), his Hendrick team-mate Kyle Larson, as well as Joe Gibbs Racing's Christopher Bell in next week's title-decider at Phoenix Raceway.
"Obviously we were not very good," said Byron, who has six wins to his name this year. "Our worst race of the year.
"Honestly, probably with 50 to go I felt really, really bad. I just had to drive the hell out of it.
"The guys stuck with me, they kept motivating me through little bits and pieces, just kind of keeping my mind straight. I'm just really thankful for them.
"It was just, yeah, a slugfest. Everyone raced me there good at the end. We just had to hang on, had to dig a little bit deeper.
"I knew when I got out of the car I was just beat. But the result means more than anything."
Byron, who won the most recent Cup race at Phoenix in March, will be part of the Championship 4 for the first time in his career. His best points result until now was sixth in 2022.
Hamlin rues Homestead power steering woes
Following his elimination from the playoffs, Hamlin remarked that the “mechanical failure last week with the power steering, that sealed our fate”.
The Joe Gibbs Racing Toyota driver had faced a 17-point deficit heading into Sunday’s race at Martinsville and, although he won the first stage and finished second in Stage 2, he was unable to get on terms with Blaney as the race ended on a 168-lap green-flag run.
Speaking after finishing third, Hamlin said. “I’m really proud of this whole team for showing up today when we really needed to, having probably a mid-50-point day. They did great. They did absolutely great.
“The #12 car [Blaney] was the best car today, so congrats to them – all the final four that made it. It’s going to be great. Hate we’re not in it.”
Last season Hamlin entered the Martinsville race with a points cushion that looked likely to carry him to the Championship 4, but Ross Chastain's dramatic last-lap wall-riding move helped him edge Hamlin for the final transfer spot.
Asked about his emotions on missing out on another chance to win his first series championship, Hamlin said, “Man, I just want to get ready and go try to win next week. I still love it so much because every week I feel like I got a shot to win.
“That’s what fuels my passion, even at my age, to keep doing this, is I’m with the team that I got that gives me such fast cars every week and gives me a chance to continue to pile on those stats before the end of my career.
“It’s not over by any means. We got a long way to go.”
Hamlin's JGR team-mate Martin Truex Jr was also eliminated from the playoffs, after leading the regular series points.
After a pitlane speeding penalty during the break between Stages 2 and 3, the polesitter was never able to recover to the sharp end and finished 12th.
Reflecting on a disappointing run in the playoffs, Truex said: “I just feel we couldn’t do anything right. If it was ever a 50/50 call, it always went against us.
“A blown engine, a flat tyre, you name it, problem after problem. Just kept setting us back, and we couldn’t get any momentum.
“I think we did a great job today. It was a tiny little error, .2 miles an hour can ruin your whole year unfortunately.”
