Kenseth earned his 25th career victory in just his third start in the JGR Toyota after leaving Roush Fenway Racing in the offseason. He took the lead away from Kahne out of a late restart and fended off Kahne’s Chevrolet over the final laps, adding another trophy to his Las Vegas victories in 2003 and 2004.

“I was real nervous all day,” Kenseth said. “(Kahne) had the best car. I told (crew chief) Jason (Ratcliff) with about 12 to go that I was sorry we were going to lose. We were just too tight. … We didn’t have the fastest car there, but we had it where we needed it to be.”

Pole sitter Brad Keselowski finished third, with hometown driver Kyle Busch in fourth and Carl Edwards fifth. Jimmie Johnson, the overall points leader, was sixth and Dale Earnhardt Jr. seventh.

Defending Vegas champion Tony Stewart finished 11th, while Denny Hamlin was 15th.

Kenseth is just the third NASCAR driver to win on his birthday, joining Cale Yarborough — who did it twice — and Busch. His win was the 50th for Toyota in Sprint Cup Series competition.

Kenseth has won at least one race in 11 of his 14 full seasons in the Sprint Cup series, but the first 13 were all in Fords with Roush Fenway, the team that gave him his break in NASCAR and fostered his development into a likely Hall of Famer. Kenseth’s decision to leave for a seat on Gibbs’ team was an open secret for much of last season, although the veteran star never really explained his move.

The 400-mile race was the first real test for NASCAR’s new Gen-6 car on the intermediate tracks they’re built to race. Although Hamlin commanded the week’s headlines when his pessimism about the car drew a stiff $25,000 fine from NASCAR, most drivers were curious how the Gen-6 would work in its ideal 1.5-mile environment.

Any drivers who still think it’s too tough to pass in the new car must not have been watching Busch, who made two lengthy charges up to early leads, doing it both before and after a pit-row speeding penalty dropped him back to 18th.

Busch charged through the field with impressive ease and took the lead out of a restart with a daredevil move on the apron with 102 laps to go. He went three wide and got underneath Kahne while kicking up dust well below the white line.

Kahne set the qualifying speed record on the Vegas track last year, but rain wiped out qualifying this week. He reclaimed the lead and held it until Kenseth nosed ahead out of another restart with 36 laps left when Kahne had trouble getting out of pit row, nearly hitting Stewart.

“I had an unbelievable car throughout the whole race,” Kahne said. “We just came out, I think, sixth (out of the pit). Tough to say we would have got by him anyway.

“I had a great day. I drove so hard every single lap today, and that’s just the new Gen-6 car. It was a lot of fun. I love it.”

The Gen-6 is still a work in progress, however. Several drivers reported various problems with their cars early on, with Clint Bowyer and Stewart both dropping far back in the opening laps. After three days of chilly weather in the desert, warmer temperatures Sunday changed the track’s feel, and teams struggled to adjust to the slickness.

Danica Patrick, the pole winner two weeks ago at Daytona, struggled with her car from the start, going two laps down by the 60th lap and later getting penalized for a tire violation. She finished 33rd.