Jimmie Johnson hasn't slept particularly well lately.

The three-time defending Sprint Cup Series champion has spent the witching hours counting worst-case scenarios instead of sheep, especially after his disastrous 38th-place finish in Texas two weeks ago.

And so, priority No. 1 heading into Sunday's Ford 400 at the Homestead-Miami Speedway for the 2009 points leader: qualifying near the front to avoid back-of-the-pack, less-experienced drivers who would be more likely to put him into the wall.

The good news after Friday's qualifying: Johnson had the fastest lap in the field and will start on the pole.

The irony: He will be boxed in by two drivers with no career wins and just nine top-10 finishes between them.

Late starting times and cooler conditions helped relative unknowns Scott Speed and Marcos Ambrose qualify second and third, respectively.

``Living through the Texas experience, I'm not taking anything for granted,'' Johnson said after earning his fourth pole of the season. ``There really is no safe approach.

``[A wreck] can happen anywhere. That's why track position is so important. It just lessens the odds.''

While anything can happen at 170 mph, both Speed and Ambrose seemed to understand the significance of the race, and their roles in it.

No driver has ever won four consecutive Sprint Cup Series titles. Short of a wreck, Johnson likely will change that Sunday.

Ambrose, who is 18th in points in his first full season on the circuit, talked about Johnson in angelic terms, claiming his No. 48 car has a halo around it.

``I'll be following him into Turn 1,'' Ambrose said. ``I guarantee he knows the line. You don't want to be the guy who takes his championship away from. I don't want to do the wrong thing by him.''

The math for Johnson is simple. If he finishes 25th or better, he will take home a record fourth consecutive title.

Mark Martin, who is second in the Chase and trails Johnson by 108 points, will start in the fourth position. He needs a win Sunday to have any shot at his first career title.

Martin held the pole position for the early stages of Friday's qualifying until Johnson ran a lap in a blistering 31.049 seconds, the equivalent of 173.919 mph.

``It is a good race car, but it wasn't a good lap,'' said Martin, who navigated the 1 ½-mile lap in 31.331 seconds. ``But I am really happy that we ran as fast as we did. Early wasn't a good time to go.''

It appeared the two front-runners and Hendrick Motorsports teammates would start side by side on the front row until the sun started to drop in the western sky.

Cooler temperatures make for a faster track, opening the door for fast laps by Ambrose and Speed, who was the last driver to take the track for qualifying.

``I think the sun going down, especially for us, helped a lot,'' said Speed, a member of the Red Bull Racing Team who is 35th in points entering the Homestead race.

``Without that, you're looking at the 5 [Martin] and the 48 [Johnson] on the front row. All things said, it was a solid lap for us, and it puts us in a great position.''

Tony Stewart, who won the Sprint Cup Series title in 2005, will start fifth, with Kevin Harvick sixth.

Miami resident Juan Pablo Montoya will start in Row 12 in the 23rd position.

The pole was a bit of the surprise for Johnson, who announced earlier in the day that he had signed a contract extension with Hendrick through 2015. He took a bad line during practice and nearly ended up in the wall.

And after Martin's quick qualifying lap, he knew that another mishap could put him back in the pack -- which is where he started in Texas two weeks ago. Johnson couldn't shake the middling drivers and paid the price, crashing in the third lap.

A similar result Sunday would undo a season of dominance.

``Race-car drivers don't typically make plans,'' Speed said, ``but certainly, you don't want to be the guy that takes out the 48. You give them room, and then race your own race.''

Johnson couldn't ask for anything more.

``I'm happy to hear that both Marcos and Scott recognize what's going on,'' Johnson said. ``Those guys have both raced for championships, and they know what it's like to get to the final race.

``I don't have any big issues.''

Any more good news and he might even get some sleep Saturday night.