Pablo Donoso might have earned his first career Firestone Indy Lights victory in the Valley of the Moon 100 at Infineon Raceway on Sunday, but the attention was diverted away by a title battle that showed the first signs of boiling over in the Californian heat.

Donoso, having been granted pole position by the random draw for reverse grid slots, led from start to finish to eventually come home 2.0601secs clear of Logan Gomez, with Ana Beatriz and JR Hildebrand next up, but it was the growing rivalry between title protagonists Raphael Matos and Richard Antinucci that grabbed the headlines.

Matos didn't come away with a race win from what he called the most important weekend of the season, but he did succeed in grasping what he covets the most - the championship points lead - after finishes of second and sixth in the double-header. The AFS Racing/Andretti Green Racing driver outpaced rival Antinucci in both events and now leads the American by three points heading into the season finale at Chicagoland Speedway on 7 September.

That weekend is sure to be full of tension, however, as Antinucci, who entered the Infineon weekend with a four-point advantage, beat Matos into the first turn of Saturday's Carneros 100, only to have to give the position back after it was deemed he had jumped the start. The rivals ran nose to tail for the remainder of the race and rounded out the podium behind winner Franck Perera.

The result was a one-point lead for Matos heading into the Valley of the Moon 100, where the Brazilian, having started seventh and made up only one place in the early going, bumped the rear of Antinucci's Lucas Oil/Sam Schmidt Motorsports entry in turn eleven of lap 27.

Jockeying for position began earlier on the lap when Matos moved to the outside of Antinucci, who held his line and forced the Brazilian into the dirt toward the end of the Esses.

"It was so far the toughest race of the championship," Matos admitted, "I had a clearly quicker car than Richard, but he never gave me any of the space I needed to make a pass. You're not allowed to block, but he blocked me four or five times. He just didn't give me enough room, and completely brake-checked me going into turn eleven. I had nowhere to go and, unfortunately, we hit each other. I am 100 per cent sure that it wasn't my fault. Of course, I'm sorry that I hit him, but you're not allowed to block."

Typically, Antinucci had a different view of the pass - and the outcome, which saw the cars swap positions to run fifth and sixth, never separated by more than seven-tenths of a second, to the chequered flag.

"In the backstraight, Matos went to the outside and cut the track so he came out right behind [me]," Antinucci claimed, "That's how he gained the advantage. I chose the inside from the beginning, knowing that he was right on my tail and I would get passed. I can't bank on having the race review that later on, so I defended my position from the inside and he chose the outside. Then he went back inside and just lifted me in the air and pushed me off. I lost two places."

For the record, Donoso became the ninth driver to win a race this season, adding to a record already established by Matos, Antinucci, Beatriz, Hildebrand, Dillon Battistini, Bobby Wilson, James Davison and Franck Perera.

"This is a beautiful day," the Team Moore Racing driver cried, "I'm pretty happy, and I love this track. I won here in 2005 [in Star Mazda], so now I've repeated in 2008. I had an awesome car. The team gave me a beautiful car, and I did the job, I finished first. But it's just not me, it's the team, my family, my manager. This is for all the people who supported me in Chile."