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For the second year in a row, the Firestone Detroit Indy Grand Prix (3:30 p.m. ET Sunday, ABC) promises to be a pivotal round in the chase for the IndyCar Series championship.

Target/Ganassi Racing's Scott Dixon still holds a commanding lead in the point standings over Team Penske's Helio Castroneves, but Helio cut the gap from 78 to 43 points with his first victory of the season last week at Infineon Raceway.

If Dixon maintains that 43-point gap after 90 laps of the Belle Isle Park street course, he will win his second IndyCar Series championship. But if Castroneves cuts the margin to fewer than 41 markers, the title contest will go down to the wire at the season finale set for Sept. 7 at Chicagoland Speedway.

A year ago, Dixon parlayed a fortuitous win at Infineon into his first points lead of the season. But his slim four-point advantage turned into a three-point deficit at Detroit when he was swept into an accident on the next-to-last lap, triggered when Buddy Rice ran out of fuel while running second. Dixon spun into the path of championship nemesis Dario Franchitti, who limped across the line in sixth place (as opposed to Dixon in eighth) to reclaim the points lead.

Last year, Dixon clearly had the momentum over Franchitti in the second half of the season. But in the last couple of races in 2008, Castroneves has looked like the man to beat, and the Brazilian is bound to be strong at Belle Isle, which in 2000 was the site of his first CART IndyCar race win -- and his first celebratory fence-climb.

Helio repeated the feat a year later in CART's final appearance on the island circuit bordered by the Detroit River.

"It's great momentum for Team Penske and a fantastic opportunity," said Castroneves. "The Ganassi guys had good momentum, a little bit of luck, and all of a sudden they are like 78 points [in the] lead. Now it's our momentum. Detroit is a great place that I enjoy very much, so we hopefully can carry some good momentum to win another one."

Castroneves took the pole at Belle Isle in 2007 on the IndyCar Series' Detroit debut and led 26 laps but crashed out late in the race. He and his teammate Ryan Briscoe figure to be the drivers to beat this year in a race promoted by Roger Penske, who has emerged as a civic leader in Detroit over the last decade.

"We know we can be fast again, and that's what we're going to focus on," Castroneves said. "We want to continue to take good chances, not crazy chances, trying to win again another race, because that's what we need to do to cut down to this chase. I know I can do it.

"Now that we have a chance in the championship, we just want to keep pushing to win races and [close] the gap between me and Scott," Helio added. "And it's the boss' track, don't forget about that!"

Dixon is coming off an uncompetitive 12th-place finish at Infineon, and surprisingly, he has not generally been the man to beat at IndyCar road races this year after dominating the genre for the last three years.

"I guess he's human, right?" noted Tony Kanaan of Andretti Green Racing, who is in his own championship battle (for third place) with Dixon's teammate Dan Wheldon. "Things go wrong for him, and it's about time -- not that we wish him anything bad. But we all had our moments this year, and then you look at the guy and he's always there. I think it makes the championship more exciting for sure for Helio."

Dixon said earlier this year that he needs to improve his road course qualifying, and starting position is perhaps more important at Belle Isle than any other road racing venue in the IndyCar Series. Passing is virtually impossible at the narrow 2.1-mile street course.

Last year, there were six cautions for 19 laps, creating plenty of opportunity for radical pit-stop strategies like the one that almost paid off in a podium finish for Rice.

Although the Belle Isle facility is much improved under Penske's management compared to when it was part of the CART series from 1993-2001, the track itself is not a favorite of the drivers because it doesn't allow for much racing.

"Personally I don't like the track -- I think it's a useless track," commented an unusually candid Wheldon. "It's very hard to overtake and it's bumpy as all get out, so it's kind of processional. [CART] had a configuration before [in 2000 and '01, when the circuit was lengthened to 2.346 miles] where you could actually overtake, and I think that would be much more valuable to the series.

"Roger Penske promotes that race and it's a great event," Wheldon added. "Everything around the race track is fantastic. It's a place I enjoy going to, but it's probably my least favorite track on the calendar."

If the race does manage to remain clean and green, traffic could be a major issue. The IndyCar Series field has grown by nearly 50 percent compared to last year, when only 18 cars made the start at Detroit.

Twenty-six cars are entered this weekend, with Milka Duno replacing Townsend Bell in the No. 23 Dreyer & Reinbold Racing entry. Tomas Scheckter and Luczo Dragon Racing return for their fifth event in 2008, while Pacific Coast Motorsports and driver Mario Dominguez have been sidelined by a lack of sponsorship.

John Oreovicz covers open-wheel racing for National Speed Sport News and ESPN.com.