Castroneves' victory, the 26th of his career in 244 IndyCar races, came by 5.5292 seconds over Scott Dixon around the 14-turn, 1.8-mile street course. Castroneves led a solid performance by Team Penske, which also produced a fifth-place finish from Ryan Briscoe in the No. 2 IZOD Team Penske Dallara/Chevrolet and a seventh-place effort from Will Power in the No. 12 Verizon Team Penske car.
The victory by Castroneves, the three-time Indianapolis 500 champion, in the No. 3 Shell V-Power Pennzoil-Ultra Team Penske Dallara/Chevrolet capped a great opening weekend for IndyCar. The series debuted its new DW12 Dallara race car and officially welcomed Chevrolet back to IndyCar and Lotus as a new manufacturer. A packed house of fans watched an entertaining race under sunny skies Sunday afternoon.
"Everything went really smoothly today," said Castroneves, who claimed his third career win at St. Petersburg to go along with his victories in 2006 and 2007. "I was just trying to be cool. These new cars are so much better in the race and faster on the starts. We're very pleased with this victory and proud of the effort from everyone. It's a great way to start the season."
After a strong final pit stop, Castroneves made the key pass of the 100-lap race when he got by Scott Dixon in Turn 1 on lap 73. He then passed JR Hildebrand a few laps later for the race lead and held Dixon at bay for the final quarter of the race to capture the checkered flag.
"It is a gratifying feeling to win, and I have to say the Shell V-Power Pennzoil-Ultra car was awesome," added Castroneves. "All the hard work in the off-season paid off. I have no doubt that Ryan and Will will join me in Victory Lane this season."
After the triumph, Castroneves paid tribute to the late Dan Wheldon by climbing the fence and touching a street sign on Dan Wheldon Way, a portion of the course named after the St. Pete resident and two-time Indianapolis 500 winner who lost his life in an accident at the 2011 season finale at Las Vegas.
"I didn't plan it," Castroneves said of the emotional celebration. "I stopped in Turn 10 and turned around and saw the sign. It was amazing. I said it before and I'll say it again - you can't explain God's mysteries. I just decided it was the perfect fit for this race and the perfect tribute to Dan."
Castroneves, who started fifth on Sunday, won for the first time since September 2010. Team Penske has now won four of the last five road- and street-course races in the IndyCar Series and has 66 road/street course wins among its total of 160 career victories - the most in the history of any team in North American open-wheel racing.
After earning a second-place starting position, Briscoe led the race for nine laps after Power, the polesitter, pitted early during the first incident of the race. Driving the IZOD machine, Briscoe fought hard to earn a top-five result - the 33rd of his IndyCar career.
"It was a very successful day for us. Congratulations to Helio and the No. 3 car guys for the win today," said Briscoe. "It was a solid finish for us with the IZOD car and great to start out the season with good points for the championship. I thought the new cars were very reliable, especially for the first race of the season, and the Chevy engine was awesome. It was a lot of fun working with the twin turbo out there, and it was good racing."
Power, who earned his 25th career pole position on Saturday, fell back in the running order after his early pit stop and found it difficult to return to the front of the field on the tough street circuit. The two-time series Road Course champion showed a lot of poise and patience and eventually worked his way back inside the top 10 before crossing the finish line in seventh place.
"I'm very happy for Helio," said Power, who won at St. Pete in 2010. "He really deserves this victory, and it's great for Team Penske to start the season with a win. Our Verizon car was very good today. We just got shuffled back a bit there after the first pit stop and we just couldn't make up the ground we needed. It was very tough to pass. We were able to gain some track position toward the end and it's good to finish seventh. We'll be back at it again next weekend at Barber (Motorsports Park)."
Castroneves gave Chevy a victory in its return to IndyCar racing after a six-year absence, and he put himself in the early lead for the IZOD IndyCar Series 2012 championship.
"You always want to start strong in the championship," said Castroneves. "But for us this means so much more."
The season resumes next weekend with the Honda Indy Grand Prix of Alabama at Barber Motorsports Park in Birmingham, Ala. Live coverage begins at 2 p.m. ET on Sunday, April 1 on NBC Sports.