1972 INDIANAPOLIS 500

The 56th 500 Mile International Sweepstakes was held at the Indianapolis Motor Speedway in Speedway, Indiana on Saturday, May 27, 1972.
Gary Bettenhausen led 138 laps until his car suffered ignition trouble on lap 176, and coasted to the pits. Jerry Grant took over the lead but pitted for new tires and fuel on lap 188 in teammate Bobby Unser’s pit - for which he would later be disqualified. Bettenhausen's Penske teammate Mark Donohue won the race, after leading the only final 13 laps. It would be owner Roger Penske's first of 16 Indy 500 victories (as of 2015).
On the morning of the race, track owner Tony Hulman asked Jim Nabors to sing "Back Home Again in Indiana" during the pre-race ceremonies. Nabors accepted and performed, without rehearsal. It was the beginning of a 36-year tradition, where Nabors performed nearly every year from 1972 to 2014.
Al Unser, Sr., who won the race in 1970 and 1971, was looking to become the first driver in history to "three-peat" at the Indianapolis 500. He fell short, but his second-place finish ties for the best three-year span (1st-1st-2nd) in Indy history.
The 1972 race was the first to utilize the Electro-PACER Light system to facilitate the yellow light periods. Speedway officials still did not utilize the pace car during cautions, and this enforcement tool would be used at Indy for seven years, albeit not without controversy in subsequent years.
After the decade of the 1960s saw numerous drivers from Europe and other nationalities, the 1972 race was the first since 1962 (and the most recent as of 2015) to have an all-American lineup. Mario Andretti who was born in Istria (part of Italy at the time) was a naturalized U.S. citizen at the time of this race. Taken from https://en.wikipedia.org/wiki/1972_Indianapolis_500 

Starting Lineup:

Row 1	Bobby Unser	Peter Revson	Mark Donohue
Row 2	Gary Bettenhausen	Mario Andretti	Joe Leonard
Row 3	Sam Posey	Johnny Rutherford	Swede Savage
Row 4	Steve Krisiloff	Lloyd Ruby	Mel Kenyon
Row 5	Jim Hurtubise	John Martin	Jerry Grant
Row 6	Mike Mosley	A.J. Foyt	Bill Vukovich II
Row 7	Al Unser	Roger McCluskey	George Snider
Row 8	Carl Williams	Dick Simon	Sam Sessions
Row 9	Mike Hiss	Gordon Johncock	Salt Walther
Row 10	Denny Zimmerman	John Mahler	Lee Kunzman
Row 11	Jimmy Caruthers	Cale Yarborough	Wally Dallenbach
Other Drivers in the Entry List:
Al Loquasto
Arnie Knepper
Art Pollard
Bentley Warren
Bill Puterbaugh
Bill Simpson
Bob Harkey
Bruce Walkup
Bud Tingelstad
David Hobbs
George Eaton
Jerry Karl
Jigger Sirois
Jim Malloy
Jim McElreath
Larry Dickson
Lee Brayton
Merle Bettenhausen
Parnelli Jones
Rick Muther
Tom Bigelow
Race Results:
Finish	Driver	Laps	Status	Prize Money
1	Mark Donohue	200	162.962	$218,763
2	Al Unser	200	160.192	$95,258
3	Joe Leonard	200	159.327	$58,793
4	Sam Sessions	200	158.411	$39,583
5	Sam Posey	198	Running	$37,411
6	Lloyd Ruby	196	Running	$29,557
7	Mike Hiss	196	Running	$30,814
8	Mario Andretti	194	Out of fuel	$24,822
9	Jimmy Caruthers	194	Running	$23,094
10	Cale Yarborough	193	Running	$22,133
11	George Snider	190	Running	$23,080
12	Jerry Grant	188	Penalty	$24,156
13	Dick Simon	186	Out of fuel	$19,759
14	Gary Bettenhausen	182	Ignition	$41,284
15	Wally Dallenbach	182	Running	$19,645
16	John Martin	161	Fuel leak	$18,084
17	Lee Kunzman	131	Lost tire	$17,901
18	Mel Kenyon	126	Fuel injection	$17,146
19	Denny Zimmerman	116	Ignition rotor	$17,320
20	Gordon Johncock	113	Exhaust valve	$17,823
21	Steve Krisiloff	102	Ignition rotor	$15,954
22	John Mahler	99	Piston	$16,013
23	Jim Hurtubise	94	Penalty	$15,350
24	Roger McCluskey	92	Valve	$15,016
25	A.J. Foyt	60	Turbocharger	$15,611
26	Mike Mosley	56	Accident	$15,984
27	Johnny Rutherford	55	Rod	$14,535
28	Bill Vukovich II	54	Rear end	$14,364
29	Carl Williams	52	Oil cooler	$14,022
30	Bobby Unser	31	Ignition rotor	$30,830
31	Peter Revson	23	Gearbox	$15,924
32	Swede Savage	5	Rod	$13,767
33	Salt Walther	0	Magneto	$14,538
Lap Leaders
1 30	Bobby Unser
31-53	Gary Bettenhausen
54-56	Mike Mosley
57-161	Gary Bettenhausen
162-165	Jerry Grant
166-175	Gary Bettenhausen
176-187	Jerry Grant
188-200	Mark Donohue