Hunter-Reay had been strong on restarts right through the afternoon, and moved into the lead on the final green flag with five laps to go.

He might have faced a late challenge from Josef Newgarden or Juan Pablo Montoya, who were just behind him, but was spared when Gabby Chaves’ engine let go a lap later and brought the yellows back out.

With insufficient time remaining to clean the track, the race finished under caution.

Just minutes earlier, Wilson had been airlifted to a nearby hospital after being struck by a large piece of debris from the car of Sage Karam, who had spun into the wall while leading.

It was by far the most serious incident in an accident-laden day: nine drivers were eliminated as the result of contact, including championship contender Graham Rahal, who was the victim of an over-optimistic move from Tristan Vautier.

Will Power had an eventful run to fourth on an afternoon that included a spin in pitlane, leaving Carlos Munoz to round out the top five.

In addition to those eliminated by crashes there was an unusually high rate of mechanical attrition.

Just 11 drivers were still running when the chequered flag flew – and one of those, Pippa Mann, was several laps down after suffering a gearbox problem.