Stewart beat Busch, his teammate in the Sprint Cup series, in a 1-2 Toyota sweep in the Nationwide season-opener at Daytona. He made it look a lot easier in the rain-postponed race at Auto Club Speedway as he led 136 of the 150 laps on the 2-mile track formerly known as California Speedway.
It is the fourth victory for two-time Cup champion Stewart in what was previously known as the Busch Series, but his first win at any track besides Daytona International Speedway.
"The car was awesome. I've got to hand it to my crew chief, Dave Rogers, and his guys," Stewart said. "They made this car real, real good and there were a lot of cars out there that weren't real good.
"We could stay out front and those other guys would wear their tires out and wear themselves out and we could just take care of our tires and do what we needed to do," Stewart added.
Both the leaders were close to running out of gas at the end, but they made it as Stewart crossed the finish line 2.408 seconds -- about half the final straightaway -- ahead of Busch.
"Tony was pretty much in a league of his own for some reason," Busch said. "Overall, having to come back from the back a couple of times, it was a good race."
By holding off Busch again, Stewart kept the 23-year-old from ending the California week leading all three of NASCAR's top professional series. Busch finished fourth earlier in the day in the Sprint Cup race, taking the points lead from Daytona winner Ryan Newman, and beat Todd Bodine in Saturday's Craftsman Truck race to grab the top spot in that series.
"Again, we passed the most cars this weekend, but they don't pay points for passing," Busch said.
"We just didn't have enough for that [No.] 20," he added, referring to Stewart. "It's kind of disappointing not to have a win, yet, but to have six top-five finishes so far this season is pretty good."
Stewart, who finished seventh in the Cup race, had to be good to beat Busch in Nationwide, where the youngster has piled up eight straight finishes of first or second and no finish worse than eighth in his last 13 starts in the developmental series.