FONTANA, Calif. — A few accidents and some bad luck since his last win had Jimmie Johnson worried he might not get a chance to defending his NASCAR Nextel Cup championship.

But a late-season surge, culminated by a victory in Sunday's night's race at California Speedway, has guaranteed Johnson a spot in the 12-man Chase for the championship and no worse than a tie for the top seed in the 10-race stock car playoff.

"I was certainly concerned," Johnson said after winning the Sharp Aquos 500, his series-leading fifth win of the season and the 28th of his career. "We had great race cars and bad luck. If you get four or five bad races in a row, you can get behind."

But, now, Johnson has joined Hendrick Motorsports teammates Jeff Gordon and Kyle Busch among the eight drivers who have clinched spots in the Chase with one more race left in the "regular season."

With team owner Rick Hendrick looking on and smiling, Johnson said, "Rick has three cars capable of winning the championship, with Kyle and Jeff and me. When I first think of the fight for the championship, I think of my teammates. There are a lot of great cars out there, but I think the three of us are going to be tough."

Johnson dominated the second half of the 250-lap event, a race that began in bright sunshine with temperatures over 100 degrees and finished under the lights with the night not much cooler. It was his first win since May 6 at Richmond.

"We've been close," Johnson said of the long victory drought. "We've been running good.

"Historically, we start the season strong, have a little bit of a struggle when we get to the warm weather and then get it going again."

This win was particularly important, with NASCAR awarding a 10-point bonus for each win this season in seeding the 12 drivers who will compete in the Chase.