On Sunday, with a crowd exceeding 100,000 for the second straight year, black clouds and a shower 20 minutes prior to the race caused a lot of excitement among the crews on the grid, as many teams changed to rain tires and back again. By the start, however, all but
Clay Regazzoni and
Derek Bell had reverted to slicks. Stewart took the lead off the grid, ahead of
Pedro Rodríguez, as Fittipaldi dropped to eighth behind Ickx, Regazzoni,
Chris Amon,
John Surtees and
Jackie Oliver. By lap 17, the Ferraris of Ickx and Regazzoni had passed Rodríguez, but by that time, Stewart's lead was nearly twenty seconds.
Graham Hill, in a privately entered
Lotus 72, came into the pits on lap 30 with fuel leaking into the cockpit, as a fitting had come loose under the seat. The team took 10 minutes to fix the leak, threw some water on Hill, whose overalls were soaked in fuel, and sent him back out. Several laps later, Hill returned to request they find him some dry overalls, as the gasoline was burning his skin. When he stopped again to change clothes, the team said they had not been able to locate any new ones. Hill, however, saw
John Surtees, who had retired on the seventh lap, sitting on the wall, and borrowed his overalls and undergarments. The two former World Champions were naked in the pits as Hill was doused with water before donning Surtees' clean clothes and returning to the track, only to retire on lap 72 with a broken clutch. At half-distance, Stewart was nearly half a lap ahead of Ickx, with Rodríguez in third and Fittipaldi about to be lapped in fourth. Ickx suddenly pitted on lap 57 to repair a broken fuel line, and he rejoined in twelfth place. He fought his way back up to fourth, setting the race's fastest lap three laps from the finish. Ickx had needed to win to have a chance of overtaking
Jochen Rindt in the Championship; his fourth-place finish would mean that Rindt would became the first posthumous Formula One World Champion. On lap 76, with a one-minute cushion, Stewart's Tyrrell began trailing smoke from its left-hand exhaust pipe. The smoke slowly grew worse, and Rodríguez tore into Stewart's lead, taking off five seconds a lap, while the
Lotus teammates unlapped themselves. On lap 83, with its oil gone, the
Cosworth engine in the Tyrrell seized, leaving Rodríguez with an 18.8 second lead over Fittipaldi, who led team-mate
Reine Wisell by another 46 seconds. At the end of the 100th lap, Rodríguez coasted into the pit lane having run out of fuel.
BRM refueled the car, but Rodríguez had lost 38 seconds to Fittipaldi, who took the lead. Rodríguez rejoined ahead of the second Lotus of Wisell. Fittipaldi recalled later, "I took the lead and, going over the finish line, I saw for the first time
Colin [Chapman] jumping and throwing his hat, something I'd seen him do for
Jim Clark and Graham Hill and Jochen, and I kept saying to myself, 'He's doing that for me. I won the race. I won the US Grand Prix!' It was unbelievable." His victory was the seventh American win for Lotus. It clinched the Drivers' Championship for the team's dead leader, Jochen Rindt, and the Constructors' Championship for Lotus and Colin Chapman. This was the final Grand Prix to be held on the layout of the track, in use since 1956.
Watkins Glen underwent extensive renovation over the course of 1971, including the lengthening of the track to in time for
that year's Grand Prix, with an interim layout adopted for the
Six Hours sports car race beforehand. == Race classification ==