Homestead, FL -- (Sports Network) - Jimmie Johnson kicked off his probable championship weekend by winning Friday's qualifying for the Ford 400 at Homestead-Miami Speedway.

Johnson, who placed 21st in the only practice of the day , turned a blistering lap around the 1.5-mile oval at 173.919 m.p.h. (31.049 seconds) for his fourth pole of the season and the 23rd of his Sprint Cup Series career. He also claimed his second pole at Homestead, with his first one here coming in 2007.

"Great effort, obviously," Johnson said. "I'm very proud of what we did today. To bounce back from 21st [in practice], I knew we were going to be better than 21st."

Johnson holds a comfortable 108-point lead over Hendrick Motorsports teammate Mark Martin heading into the season-ending race. If Johnson finishes 25th or better, he will clinch his unprecedented fourth straight Cup championship, regardless of Martin's performance.

"Qualifying trim on Friday is so different than what we will have tomorrow and then moving on to Sunday," Johnson said. "We'll use the momentum for sure, but we don't want to get cocky or too confident in what we did today, because tomorrow is a new day with a new set of challenges."

Earlier in the day, Johnson and team owner Rick Hendrick announced Johnson's contract extension with Hendrick that will keep him with the organization through the 2015 season.

Martin will start in the fourth position. The 50-year-old Martin is attempting to become the oldest driver to win a Cup title. He has finished second in points four times (1990, '94, '98 and 2002).

"It was a great race car, but it wasn't a great lap," said Martin, who went out sixth in qualifying.

Rookie Scott Speed, the last of the 48 drivers to qualify, surprisingly took the outside pole after posting a lap at 172.695 m.p.h. Speed also qualified second in last year's race at Homestead.

"I think more than anything it was just a product of going out when the sun was going down," Speed said. "Nonetheless, it's two years in a row that I sat on the front row here, so eventually I want to be on the pole."

Marcos Ambrose qualified third, and Tony Stewart secured the fifth spot.

Kevin Harvick, Ryan Newman, Greg Biffle, Bill Elliott and Clint Bowyer completed the top-10.

Joe Nemechek, Dave Blaney, Mike Skinner, Max Papis and David Stremme failed to qualify.

Sunday's 400-mile race is scheduled to begin around 3:15 p.m. (et).