The reigning NASCAR Nextel Cup champion passed Tony Stewart three laps from the end today at Atlanta Motor Speedway and went on to win his second straight race.

''We're thinking championship already,'' said Johnson, only four races into the 36-race season. ''That's really the mode anymore. You have to think about points and being in the top 12 all the time.''

Johnson had the car to beat today, leading 132 of the first 238 laps. But the only laps he led the rest of the way in the 325-lap event on Atlanta's 1.5-mile oval were the last three.

The 25th victory of his Cup career moved Johnson within 28 points of current series leader Mark Martin, who plans on skipping next week's race at Bristol and the race the following week at Martinsville.

That would leave Johnson just 20 points behind Hendrick Motorsports teammate Jeff Gordon and 17 behind Jeff Burton going into Bristol, the fifth of the 26 races that will determine the 12 drivers in the Chase for the championship.

''Right now, it's easy to feel good about things and there no doubt that the championship is what's on our minds,'' Johnson said. ''When you come into the sport, you focus on victories and top 10 and now the Chase is a big mark for the teams to make.

''But, after you win a championship, I think it changes you a little bit and that's what you really focus on and what you want to do again and again. Since we came into '07, the team meetings and discussions, everything is about trying to win another championship. Right now things are going good and we're doing the right things, but it's way too early to get too excited.''

Johnson, who overcame a penalty in the pits at Las Vegas to beat Gordon the previous week, had some problems with tire wear late in today's Kobalt Tools 500.

Stewart, a two-time Cup champion, appeared on the way to his first victory of the year after coming off pit lane ahead of Matt Kenseth and third-place Johnson after the final stops by the leaders during a caution flag on lap 311.

After the green flag waved with 11 laps to go, Johnson took just three laps to get past Kenseth, then took off after Stewart in the duel of Chevrolets.

Johnson pulled side-by-side with Stewart just past the finish line on lap 322. Johnson then got his nose out ahead and, as the two cars drove through turn two, Stewart scraped the wall.

Johnson easily led lap 323 and continued to pull away from Stewart, going on to win by about half the front straightaway. He credited crew chief Chad Knaus for making some key adjustments on the last pit stop.

''At the end, when it came time to race for checkered, Chad made some great adjustments to help me on the short run,'' Johnson said. ''That's the one thing I was lacking compared to the 20 (Stewart). At the beginning of a run he had a little more grip and could drive a little harder.