Ryan Briscoe has taken the lead from Dario Franchitti as the Indianapolis 500 passed its quarter-distance point.
Franchitti had led much of the opening part of the race having overtaken pole-sitter Helio Castroneves as the green flag flew after an early yellow for Marco Andretti and Mario Moraes' collision.
Castroneves then lost out to Briscoe at the first pitstops, and subsequently fell behind Scott Dixon, although the Penske and Ganassi cars continue to run together in a lead quartet, with Andretti Green's Tony Kanaan just behind.
Graham Rahal was also hanging on with the leaders until becoming the race's latest retirement when he slammed into the wall a few laps ago in a crash that elevated top rookie Raphael Matos into the top six.