Wheldon is second in the overall standings behind Castroneves

The Briton was bidding to become the first IndyCar Series driver to win at the same track three years in a row.

Victory for pole-sitter Castroneves gave him his second straight IndyCar Series win of the season.

The Brazilian, who won the Honda Grand Prix of St Petersburg earlier this month, finished 6.3851 seconds ahead of Wheldon in the 200-lap race.

"It's a reasonable result from a points standpoint," said the Emberton-born Wheldon, who drives for Ganassi Racing.

"I just didn't have enough for Helio. At some points of the race I was very, very quick and just tailed off at other points.

"All in all it's a great result. It would have been great to win three in a row. But it just wasn't meant to be and we'll move on to Indy."

With rain wiping out qualifying, Castroneves started from the pole because he led the IRL championship going into the race at the Twin Ring Motegi circuit north of Tokyo.

After securing victory, he jumped out of his Honda-powered Dallara and climbed the fence in his trademark victory celebration.

Scott Dixon was in second place for most of the race but fell out of contention after a delay during his final pit stop after 148 laps.

Brazilian Tony Kanaan finished third, followed by Sam Hornish Jr, Buddy Rice and Bryan Herta.

Castroneves extended his lead in the championship standings with the win, moving to 146 points, 42 ahead of second-placed Wheldon.

Scotsman Dario Franchitti was 11th for Andretti Green.