The New Zealand driver Scott Dixon led from start to finish at the latest round of the Indy Car series in Motegi but it was Australian Will Power who seized the series lead with a second placing at the Japanese event.
Crucially for Power, Dixon's team-mate and defending series champion Dario Franchitti had another frustrating day, finishing eighth after being penalised for hitting Australian Ryan Briscoe's car on the 26th lap.
Power now has an 11-point lead over Franchitti with just two rounds remaining, oval races in Kentucky and Las Vegas.
With two wins and a second from his past three races, the Australian is in pole position for a maiden Indy Car championship title.
But after surrendering the championship to Franchitti in the final event of last year's series, Power knows not to get too far ahead of himself.
Power moved to 542 points, 11 ahead of Franchitti (531), with Dixon (483) keeping his faint championship hopes alive with a second victory of the season.