The reigning NASCAR Nextel Cup champion came on strong at the end of Sunday night's 250-lap race, grabbing his series-leading fifth victory of the season, clinching a spot in the Chase for the championship and guaranteeing he will be no worse than a tie for the top seed in the 10-race playoff.

Johnson dominated the second half of the Sharp Aquos 500, 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 his first win since May 6 at Richmond.

"We've been close," Johnson said of the long victory drought. "We've been running good. But it was nice to get the job done tonight.

"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. It seems like that's the way it's going and I'm just glad to be back in Victory Circle."

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. If the Chase began next week, Johnson would be the top seed, with 10 more points than Hendrick Motorsports teammate and series points leader Jeff Gordon, who has four wins.

"We're fortunate to be in that situation," Johnson said. "That's very satisfying. The season is all about a championship, especially when you get in the Chase. It's time for the pressure to pick up and the hard work to start. And my guys are ready for it."

There was some shuffling at the bottom of the Chase contenders, with Martin Truex Jr. and Kurt Busch each moving up one spot to 10th and 11th, respectively, while Daytona 500 winner Kevin Harvick slipped from 10th to 12th.

Dale Earnhardt Jr., began and ended the race in 13th, despite a solid fifth-place finish. But he did cut his margin from 158 behind Busch coming in to 128 behind Harvick heading into next Saturday night's race at Richmond, the final event before the start of the stock car playoff.

"It was so hot out there you kind of get aggravated," said Earnhardt, who looked completely drained after getting out of his car. "I'm tired, real tired."

Told his point deficit heading to Richmond, Junior said, "I don't know much about the system, I never cared to. I just go out there and run as hard as I can. It doesn't look like we're going to make it, but we're not going to quit trying until they tell us we're not (in it)."

Johnson, who took the lead for good after a series of green flag pit stops 22 laps, led 65 of the last 82 laps on the two-mile oval. He easily held off runner-up Carl Edwards in the waning laps, although it appeared for a while that Edwards might overtake him.

"I thought he was going to be a sitting duck," said Edwards, who overcame a pit collision with rookie Juan Pablo Montoya early in the race. "I said on the radio that I thought it was going to be me and Kyle (Busch). It's immensely disappointing. Running second is terrible."

Kyle Busch finished third, followed by Jeff Burton, Earnhardt, Matt Kenseth, Truex, Brian Vickers and Kurt Busch. Harvick finished 13th.

Kurt Busch, who started from the pole, was happy to be closer to clinching a spot in the Chase - 13 points ahead of Harvick and only 20 behind Truex in 10th and 25 behind Clint Bowyer in ninth.

"I feel pretty solid," he said. "You know there's a guy behind us now to give us a little bit of cushion. It's going to be an interesting race in Richmond."