It's now or never for Denny Hamlin

Denny Hamlin has been stuck on mediocrity in his five races this Sprint Cup season, with finishes that have ranged from 17th at Daytona to 29th at the Auto Club Speedway in California. He should break out of his mini-slump on Sunday when the series races at Martinsville, Va.

Hamlin isn't thinking top-five at Martinsville. He's thinking win and won't be satisfied with anything less. He's the biggest threat to stop the amazing Jimmie Johnson, who has won six of the last 11 races at the .526-mile track and three of the past four overall this season.

Johnson and Hamlin have split the past four wins at Martinsville and they took their rivalry there to new level last year. Hamlin's FedEx Toyota led 296 laps last spring, but Johnson knocked him out of the way with 16 to go and beat him by a couple of car lengths. It stung Hamlin, who clearly didn't believe Johnson's assertion that the contact was unintentional.

In the fall, Hamlin ran down Johnson during a 136-lap green-flag run to take the lead with 139 to go and led the rest way with Johnson chasing him. There was drama at the end, with three restarts in the final 17 laps including a green-white-checkered. Double-file restarts helped and Hamlin didn't give the Lowe's Chevrolet a chance to get a bumper to him

"You actually feel a little bit better with him being on the outside of you than you do right behind you on a restart," Hamlin said.

Hamlin has finished sixth or better in his last seven starts at Martinsville. He's been outstanding on flat tracks since his first full Cup season in 2006. Of his eight victories, three were at Pocono, two at Martinsville, one at New Hampshire and one at Richmond.

Many pundits expected Hamlin to be Johnson's primary challenger for the Sprint Cup this year, based upon a career-high four wins including in the finale at Homestead-Miami. That one was a breakthrough because it's a 1.5-mile intermediate-banked track. There's plenty of time remaining to challenge Johnson, but Hamlin needs to start his turnaround at Martinsville. If not there, where?

"Denny (Hamlin) has been awfully strong there," Johnson said. "I know the 24 (Jeff Gordon) will be. And a few other guys have been sorting things out there."

Hamlin is my pick to win on Sunday, but Gordon, Kevin Harvick, Tony Stewart and Dale Earnhardt Jr. also have a chance to derail the Johnson Express.

Here they are, in order of probability:

Gordon: He's been a contender in the eight races since his seventh victory at Martinsville in the fall race of 2005, all top fives including second-place runs behind Stewart in the 2006 sprint, Johnson in 2007 and Hamlin in 2008. Gordon has led between 36 and 165 laps in the last seven races. You've got to think he's going to figure out how to complete the job soon.

Harvick: He doesn't have a particularly strong record at Martinsville, with no top-fives and seven top-10s in 17 starts, but he's clicked with crew chief Gil Martin in their first full season together. Harvick is leading the points and has a couple of seconds. His 11th last week at Bristol was his worst result. In the final year of his contract with Richard Childress Racing, he's undoubtedly highly motivated. Five of Harvick's 11 Cup wins have come on flat tracks: two at Phoenix, one at New Hampshire, Richmond and Indy. He's also won Nationwide and Camping World Truck Series races at Martinsville. Without a win in his last 112 Cup starts, Harvick won't be reluctant to use his bumper on Sunday.

Stewart: He has two wins at Martinsville: in 2006, when he led 288 laps, and in 2000, when he led 179, but he hasn't led a lap in the past five races. Still, he's managed to put together solid runs, including third in the spring and ninth in the fall with crew chief Darian Grubb at Stewart-Haas last year. They should be able to build on those performances Sunday. Stewart is fifth in the points, so there's overall strength in the program, and it's not even June yet.

Earnhardt Jr.: He's winless in 20 starts, but has eight top-fives and finished second in the fall race in 2008. Junior and crew chief Lance McGrew are showing real progress. Earnhardt's speeding penalty last week at Bristol cost him at least a top five, but he rallied from 26th to finish seventh in an impressive drive. The Junior Nation will celebrate soon and it could be Sunday.