Scott Dixon's hopes of defending his IndyCar title took a big hit at the latest race in St Louis yesterday.

The Kiwi driver and five-time IndyCar champion was forced to withdraw during the race after suffering a radiator leak in the opening lap.

Dixon remains fourth on the driver's standings with 493 points, 70 adrift of leader Josef Newgarden with just two races remaining.

IndyCar drivers earn 50 points for a win, with the season's final race worth double points.

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Takuma Sato held off Ed Carpenter to win the race, his second victory of the season. Tony Kaanan was third, followed by Santino Ferrucci and Simon Pagenaud.

Pole-sitter Newgarden spun coming out of Turn 4 of the last lap and finished seventh.

Sato won by 0.399 seconds. The victory comes on the heels of his highly scrutinised move on the first lap at Pocono last week that helped trigger a major accident.

Sato denied Team Penske a sweep of the ovals this season and gave Rahal Letterman Lanigan Racing a sorely needed win. Defending race champion Will Power finished last after he crashed in Turn 4 of lap 54.

IndyCar's next stop is Portland on September 1.