Parnelli Jones had the pole position on May 30, 1963, after a near-victory the year before. (He'd also broken the 150-mph barrier during qualifications with a one-lap record of 150.729 mph and a four-lap average of 150.370 mph in '62.)
Jones' front-engine Offy 4-cylinder dominated, but the rear-engine Ford Fairlane pushrod V8 in rookie Jim Clark's Lotus was a serious challenger. Clark led from Lap 68 until he pitted on Lap 96. During the last 50 laps, he once again closed the gap with Jones, setting the scene for a dramatic finish.
With 20 laps to go, Jones' car began smoking, having spewed oil from a horizontal crack in the external overflow tank at the rear of the car for several laps. Observers reported increasingly thick smoke and dripping oil in the corners.
Clark's team owner, Colin Chapman, reminded Chief Steward Harlan Fengler of the protocol, explained during the prerace drivers meeting, that cars losing oil would be black-flagged. However, Jones' team owner, J.C. Agajanian, argued — in a heated exchange at the start/finish line — that his car should be allowed to continue because the oil leak was minor and, having dropped below the level of the crack, had subsided.
It wasn't true. Clark slowed, settling for second place rather than risk spinning out in the oil still spilling from Jones' car. Two drivers following Jones did spin in his oil. When Eddie Sachs, who spun in Turn Three, confronted Jones the next day, Jones punched him in the face. Roger McCluskey, in third place, spun in Turn Two on the last lap, bringing out the yellow flag.
Chapman accused USAC officials of a bias for the American driver and car. Had Fengler black-flagged Jones, per the rules, Clark would have won that day. However, Fengler insisted that the car had ceased leaking and that he didn't want to "take this race away from a man [based] on a snap judgment."
The Lotus team declined to file a formal protest.