The Aucklander finished 4.2 seconds in front of defending champion Hiroaki Ishiura. The pair outdistanced the field, with third placed Yuji Kunimoto finishing more than half a minute behind.

Cassidy is contesting his second season in Japan's premier formula in a 600 horsepower Toyota powered single seater.

His victory has taken him to within a point of championship leader Naoki Yamamoto, who could only finish eighth.

Cassidy led from the start and only Ishiura could stay near him as the pair used soft compound tyres to draw away from the rest of the field, which included Toyota works drivers Kazuki Nakajima and Kamui Kobayashi, fresh from their Le Mans success, who finished fifth and 12th respectively.

Apart from his pit stop to change to fresh medium tyres, Cassidy, the double Toyota Racing Series champion and defending Super GT titleholder in Japan, led throughout the 55 laps.

The Kondo team was jubilant, as it was their first victory in ten years in Japan's top single seater category.

Cassidy had been in fine form throughout the meeting, grabbing pole position late in qualifying in the wet conditions on Saturday. Sunday's race was in dry conditions and he was equally dominant.

The result has put the 23-year-old right into contention to win the championship, with three rounds to go. The next race is at Motegi on August 19.

Results, Super Formula, Round four, Fuji Speedway, 55 laps:

1, Nick Cassidy;

2, Hiroaki Ishiura, +4.286 seconds; 3, Yuji Kunimoto, +32.746

4, Ryo Hirakawa, +35.306;

5, Kazuki Nakajima, +43.512.

Series Points:

1, Yamamoto, 22; 2, Cassidy, 21; 3, Nakajima, 11.