FONTANA, Calif. — When dark clouds ominously obscured majestic Mount Baldy north of Auto Club Speedway early in Sunday’s race, NASCAR’s drivers all realized they were probably in for a short day on a long track.

Nobody did a better job racing until the raindrops fell than Tony Stewart.

Stewart got his second NASCAR victory of the season when rain shortened the race at Auto Club Speedway by 71 laps, extending the defending Sprint Cup champion’s unusually strong start.

Kyle Busch finished second, and Dale Earnhardt Jr. added to his good start to the season in third.

“You hate to have it end with rain like that,” Stewart said. “ But we’ve lost some that way, and we didn’t back into the lead.”

Stewart has won seven of the last 15 races, including Las Vegas last month, in a remarkable stretch of dominance for a driver who rarely gets rolling until summer.

Although Stewart sees nothing special about his approach to the new season, he’s clearly focused. Stewart and new crew chief Steve Addington didn’t mention the rain to each other until moments before it hit one end of the 2-mile oval, but they had already done the work necessary to win.

Stewart’s Chevrolet passed Busch 44 laps before the race was stopped when the looming rain clouds finally burst and halted a race run entirely on green flags to that point. Although a few drivers weren’t happy when the race was called off after a delay of just over 30 minutes amid steadily worsening rain, Stewart collected his 46th career win and his second at Fontana.

“Playing to the weather, everybody is trying to get everything they can get toward the midway point of that race,” Stewart said.

Defending race winner Kevin Harvick was fourth, and Carl Edwards was fifth. Greg Biffle, Edwards’ Roush Fenway Racing teammate, finished sixth and kept a seven-point lead on Harvick atop the points standings.

The drivers saw only blue skies at their meeting two hours before the race began, but the weather steadily worsened. The resulting drop in temperature threw off many teams’ calculations on air pressure and other decisions, forcing adjustments on their first pit stops.

After hitting the wall late in last week’s race at Bristol, Stewart was back in top form. He earned his earliest win in a NASCAR season two weeks ago at Las Vegas with an aggressive move out of a restart, but the real racing at Fontana hadn’t even started before rain hit.

“We didn’t have an opportunity to do anything other than what we had planned from the start,” said Earnhardt, who has finished in the top 15 in all five races this season.