Experience has taught Johnson never to let his foot off the gas

It looks so easy now.

The rare sports feat of a championship repeat is there for the taking. Jimmie Johnson has done all he can do.

He will start at the front of the Ford 400 field Sunday. The one man he has to worry about -- Jeff Gordon -- will start five rows behind him.

Johnson needs to finish 18th or better to secure his second consecutive Nextel Cup title in the No. 48 Chevrolet.

His team and his driving have been flawless the past month as he tied the modern-era record with four consecutive victories to build an 86-point lead with one race to go.

It all just looks so easy now. And that scares the heck out of Johnson.

"I feel we've done a good job with the things we can control," Johnson said. "But the things we can't control are what worry me. Incidents on the track, tire issues, whatever, that part concerns me."

Johnson knows all too well what can happen when you least expect it. Two years ago at Homestead-Miami Speedway, Johnson's championship chances ended when he blew a tire and hit the wall.

He entered the final race 52 points behind Tony Stewart. But Johnson started falling back on the track when he felt the tire going down.

Crew chief Chad Knaus decided Johnson had to stay on the track and hope for a yellow flag rather than pit under green and go two laps down.

No such luck. The tire blew and the season was over, the third consecutive year Johnson had come close to a title without finding a way to win it.

The disappointing end to 2005 caused a rift between Johnson and Knaus that team owner Rick Hendrick thought was unsalvageable. Johnson saw it differently.

"I'm not going to sugarcoat it," Johnson said. "We were frustrated with each other. It wasn't working. I'm sure Rick thought things were falling apart.

"But I didn't want another crew chief and he didn't want another driver. We never lost belief in each other. We just needed to hash it out."

Repairing a relationship was something Johnson could control. With Hendrick's help as an arbitrator, no two guys ever hashed it out better.

Johnson won five times in 2006 on the way to his first championship. He has 10 wins this year, getting it done when it counted down the stretch.

Johnson could coast home now. He's one step from the mountaintop. Things are almost perfect.

"You can't believe that," Johnson said. "In my life in racing, every time I've been comfortable and think I have everything under control, it bites me."

Once bitten, twice shy. He won't take the green flag Sunday feeling the title is locked up. Johnson knows that so many odd things can happen in a race, and that some of them could ruin his day.

"I've had too many experiences like that," Johnson said. "I have a little trigger in my head that keeps me on my toes. I chase those thoughts [of having a lock on the title] out of my mind and try to keep my guard up."

Does keeping his guard up mean playing it safe? Johnson hasn't done that throughout the Chase. He has raced to win every week, including a spectacular battle with Matt Kenseth to earn a victory at Texas Motor Speedway two weeks ago.

But this situation is different.

"The big picture," Johnson said. "We have to keep in mind the big picture. I will try not to make a stupid mistake and cost us the championship. The one thing I feel we've done in maturing as a race team is finding where the limit is. You have to be smart and drive within the limits of the vehicle."

The limits of the 48 Chevy were higher than those of any other car on the track the past four weeks. Johnson would love to get that fifth consecutive victory, but he also will play it safe and not push the limits.

Jeff Burton believes playing it safe can result in unwanted consequences.

"How many football teams have we seen get beat because they were playing prevent defense," Burton said. "There's a big difference between giving 100 percent and 98 percent. And if you only give 85 percent, that's when you get in trouble.

"But Jimmie and Chad know what they're doing. If they just go out and execute the way they've done most of the year, they'll be fine."

It looks so easy now, but not to Johnson.

"It's still very stressful," he said. "The pressure's still there, but being on a roll helps calm a lot of that down. I still have doubts, but those doubts motivate me."

Terry Blount covers motorsports for ESPN.com. He can be reached at terry@blountspeak.com.