Updated

It ain't over till it's over.

That's the mindset of Jimmie Johnson heading into this weekend's Sprint Cup Series season-finale at Homestead-Miami Speedway.

Johnson fell 20 points behind leader Brad Keselowski after finishing 32nd in last Sunday's penultimate race at Phoenix due to an accident in the late going. Keselowski had trailed Johnson by seven points, but after his sixth- place finish at Phoenix, he is now in the driver's seat to win the Chase for the Sprint Cup championship.

"Certainly if you have the choice you always want to be in the lead of the points, especially in the closing races, so I'm thankful for that," Keselowski said. "But I also know that the troubles that (Johnson's team) had are the same troubles that we could have (this) week, and so you try not to take anything for granted. You try to just focus on what lies ahead, and we've got to do the best job we can at Homestead."

Keselowski and Johnson are the only drivers who remain in title contention. The other 10 members in the Chase field have been mathematically eliminated.

Keselowski will clinch his first Sprint Cup championship if he finishes 15th or better at Homestead, regardless of Johnson's performance there. Keselowski can also be guaranteed the title if he finishes 16th and leads at least one lap or places 17th after leading the most laps.

Johnson has battled back from a points deficit with one race to go to win the championship in the past. Two years ago, he trailed Denny Hamlin by 15 points, which is roughly four under the current points system. Johnson's second-place finish compared to a 14th-place run for Hamlin allowed Johnson to claim his record-extending fifth consecutive title.

"My focus is going down there and winning the race," Johnson said. "We typically haven't had to have that mentality going into this race, but we have shown we can race for the win. We did it in 2010 against Denny, finished second and won the championship. This 48 Lowe's team can do it again. We have nothing to lose and can gamble and take chances. Brad doesn't have that luxury. This isn't over. This team never gives up, and we don't intend to now."

Johnson has yet to win in his 11 races at Homestead. Keselowski, though, has finished no better than 13th in his four starts there.

If Keselowski can win the championship, the 28-year-old would give team owner Roger Penske his first title in NASCAR's premier series. Keselowski's 2010 Nationwide Series championship was Penske Racing's maiden title in a NASCAR national touring circuit.

"When I first came to Penske Racing, I viewed it as an organization with so much potential," Keselowski said. "I had a vision for what I knew this place could become, and I shared that with Mr. Penske in our first meeting together. And as he began to give (crew chief) Paul (Wolfe) and I the things that we needed, we began to show results on the racetrack which, in turn, led to a lot of trust among myself, Mr. Penske, Paul and everyone else at Penske Racing.

"So having a legitimate shot to win the championship this weekend is something that I take great pride in because I know we got there together."

Keselowski also has an opportunity to hand Dodge a huge going-away present before the auto manufacturer bids farewell to NASCAR competition, at least for the time being. Keselowski is seeking to become the first Dodge driver champion since Richard Petty in 1975. The auto maker departed the sport after the 1977 season and returned in 2001.

"I would hope that they come back as soon as possible," Keselowski said. "I would love to see that happen. I think it's important for the sport to have as many participating manufacturers as possible, especially one that fits the sport as Dodge does. I don't have a good feel for their vibe on it, but I hope to see them back soon."

Penske Racing will field Fords for its Sprint Cup and Nationwide teams in 2013 and beyond.

If Johnson can pull off a remarkable comeback to win the championship, it would be the record-extending 11th title for team owner Rick Hendrick. A sixth championship for Johnson would put him one behind the series record for most titles, shared by Petty and Dale Earnhardt.

Forty-eight teams are on the preliminary entry list for the Ford EcoBoost 400.

Series: NASCAR Sprint Cup. Date: Sunday, Nov. 18. Race: Ford EcoBoost 400. Site: Homestead-Miami Speedway. Track: 1.5-mile oval. Start time: 3 p.m.(ET). Laps: 267. Miles: 400.5. 2011 Winner: Tony Stewart. Television: ESPN. Radio: Motor Racing Network (MRN)/SIRIUS NASCAR Radio.