The 55th 500 Mile International Sweepstakes was held at the Indianapolis Motor Speedway in Speedway, Indiana on Saturday, May 29, 1971. Al Unser, Sr. won for the second consecutive year, dominating most of the race. The race was marred by a crash involving the pace car at the start. Eldon Palmer, a local Indianapolis-area Dodge dealer, lost control of the Dodge Challenger pace car at the south end of the pit area, and it crashed into a photographers' stand, injuring 29 people, two seriously.

Peter Revson started on the pole with a speed of over 178 miles per hour, more than a mile per hour faster than any other qualifier, with defending champ Al Unser in the middle of the second row. Mark Donohue, who qualified in the middle of the front row, took the lead at the start of the race and led the first 50 laps. A mechanical issue ended his day after just 66 laps, and Unser assumed the lead. He and Joe Leonard swapped the lead several times during the middle portion of the race, but Unser led for the final 83 laps, giving him a win for the second year in a row.

Unser (born on May 29, 1939) became the first and only driver to date to win the race on his birthday. It was his second of an eventual four Indy victories. Unser also became the first winner to celebrate in the new victory lane. The new winner's area, now featuring black and white checkered ramps, was moved from the south end of the pits to the "horseshoe" area immediately below the Master Control Tower, near the start/finish line.

The 1971 Indy 500 was part of the newly re-organized USAC Marlboro Championship Trail, in which dirt tracks were separated from the paved ovals and road courses. From then on, the Gold Crown championship schedule would consist solely of paved tracks (both ovals and road courses), giving the national championship a decidedly new look for the 1970s and beyond. In addition, with 500-mile races at Ontario and Pocono now on the schedule, Indy car racing formed its first "triple crown."

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