Sunday's Indy Grand Prix of Sonoma saw the battle for the 2006 IRL IndyCar Series title take another couple of twists and turns that have left just 21 points separating the four remaining championship hopefuls with one round to go.

The series finale in Chicagoland in two weeks time is almost guaranteed to be a classic after Marlboro Team Penske teammates Helio Castroneves and Sam Hornish Jr. exchanged the IndyCar Series point lead for the fourth consecutive race during the Infineon Raceway weekend.

A single-point separates the pair, with Castroneves ahead, who have an identical number of wins (four), second-place finishes (one) and third-place finishes (one) through the 13 IndyCar Series events.

"Let me tell you, it's no question it's a situation that it's really close," said Castroneves, who leads Hornish following a fifth-place finish in the Indy Grand Prix of Sonoma. "We came here to take as much points as we could. This is part of the game, which is fun. Now let's go to Chicago. It's kind of every man for himself."

Castroneves, however, doesn't have his eye on just his teammate. Trailing behind the Penske duo are Target Chip Ganassi drivers Dan Wheldon and Scott Dixon, who are 19 and 21 points back, respectively. Castroneves knows a mistake could open the door for a title rival other than Hornish.

"We don't want to give the championship to Target (Chip) Ganassi," Castroneves said. "We're going to try everything we can to win this championship, whether it's going to be me or Sam. My opinion, obviously it should be me (laughter), but I don't think Sam would agree with that."

The Target duo recorded a fourth (Dixon) and sixth (Wheldon) at Infineon, and though title hopes are dwindling, neither Dixon nor Wheldon is ready to concede the title.

"As fast as we've been all year, and as aggressive as everyone knows I can be, no one is going to want to mess with me in Chicago," Wheldon said. "I have nothing to lose now, and I'm not ready to give up and neither is the Target team. We're still in this. We just have to win at Chicago and the rest will be in the "Racing Gods"' hands. We've worked very hard all year to make a championship possible, and it's not over yet."