Engine failure in the latest IndyCar race in Wisconsin has shunted New Zealand's Scott Dixon from second to fifth in the series standings.
Dixon's Chevrolet struck problems on the seventh lap of the Kohler Grand Prix, leaving pole-sitter Will Power with a clean run to win at the Road America Circuit.
Australian Power held off a late charge from Tony Kanaan to clinch successive race wins after going more than a year without a victory for Team Penske.
Dixon was pushing Power hard early on before problems struck his Chip Ganassi Racing machine.
"It's a real bummer," he said.
"The car was so fast. It would have been a hell of fight between us two (Dixon and Power), and unfortunately we came up short."
Dixon's series title defence takes a blow after nine of 16 rounds.
He drops to 90 points behind French leader Simon Pagenaud and is surpassed by Brazilian Helio Castroneves, Power and American Josef Newgarden.
Standings: Simon Pagenaud (France) 375, Helio Castroneves (Brazil) 301, Will Power (Australia) 294, Josef Newgarden (USA) 292, Scott Dixon (NZ) 285, Tony Kanaan (Brazil) 280.