Chicago - American pole-sitter Josef Newgarden pulled away at the start in capturing Sunday's IndyCar Road America Grand Prix, giving the defending season points champion his 10th career triumph. 

Newgarden dominated on IndyCar's longest course for his third victory of the season over 55 laps at the 4.014-mile, 14-turn road course at Elkhart Lake, Wisconsin. 

American Ryan Hunter-Reay was second with New Zealand's Scott Dixon third and Japan's Takuma Sato fourth. 

Newgarden won two of the first four races of the campaign at Phoenix and Alabama, but had placed no better than eighth in five races since then. 

"It was pretty flawless," Newgarden said. "This car has been a rocket all week. It was not easy. Ryan was really pushing me all of the time. I knew what I had to do but it wasn't easy." 

Newgarden and Hunter-Reay surged at the start as disaster struck Indianapolis 500 winner Will Power of Australia, the 2016 Road America champion who started alongside Newgarden in the front row. 

Power was slowed at the green flag with a broken right header and pitted quickly before finishing last in the field of 23. 

France's Sebastien Bourdais, the 2007 Road America winner who started sixth, also fell back early with electrical issues. 

Dixon, last year's Road America winner, moved into third after pit stops with 26 laps remaining and made his last refuel stop a lap before Newgarden and Hunter-Reay. 

But the Americans returned to the track just ahead of him and Hunter-Reay never threatened a pass over the final 13 laps. 

"I wasn't able to catch up to Josef. He was in the zone for sure," Hunter-Reay said. "I was pushing 110 percent. That's just what we had." 

Dixon, who started eighth, stretched his season points lead from 23 to 45 points after 10 of 17 races with his sixth consecutive podium finish. 

"It was OK," Dixon said. "If we had done better in qualifying... I think we would have had a real good shot at winning this race." 

Dixon, 37, seeks his fifth career IndyCar season title after taking the crown in 2003, 2008, 2013 and 2015. 

Newgarden, who won four times last year on the way to his first IndyCar season points title, pulled within 50 points of Dixon. 

"It's far until we get to the end of the season," Newgarden said. "I think we're going to be just fine. we'll be there at the end." 

The next race will be July 8 at Iowa, where Hunter-Reay is a three-time winner and Newgarden won in 2016.