First half Rain fell the night before the race, and the weather forecast for race day was bleak. However, in the morning, the skies cleared, the track dried, and the race began on-time as scheduled. At the start,
Al Unser Sr. swept from the outside of the front row, and led the field into turn one. Unser was driving
Jim Hall's radical new
Chaparral 2K chassis. He pulled out to a commanding lead, and proceeded to lead the first 24 laps. Heavy attrition early on saw seven cars out with mechanical problems (
Janet Guthrie the most notable) by lap 22.
Cliff Hucul stalled on lap 28, bringing out the first caution during the first sequence of pit stops, ushering in the modern era of caution flag/yellow light procedures. As the field went back to green,
Al Unser again dominated. On lap 43,
Wally Dallenbach lost a wheel down the backstretch, and had to precariously guide his car back to the pits on three wheels. The car was too heavily damaged to continue however. With Al Unser still dominating, the rest of the top five was
Rick Mears,
Bobby Unser, and
Johnny Rutherford. Rutherford then headed to the pits with a broken gear. After lengthy repairs, he returned to the race. Leader Al Unser came in for a routine pit stop under the caution on lap 97. Moments later, he was back into the pits after it was reported that something may have been leaking or smoking from the back of the car. Still under the caution, after a quick consultation, Unser returned to the track. The green flag back came out with
Bobby Unser now leading.
Second half On lap 103,
Al Unser Sr. was running second to
Bobby Unser when heavy smoke and flames started coming from the back of the car. The
Chaparral 2K experienced a failed transmission oil fitting, and Unser was out of the race. After mutual differences, Unser decided to leave the team at the end of the season. In two seasons with the Jim Hall team Unser had won three out of six five hundred mile races (all 3 500 mile races in 1978) giving him a 50% win rate for five hundred mile race wins in two years. With
Al out, his brother
Bobby was now in control.
Rick Mears was holding second, and
A. J. Foyt was moving up to third, one lap down. The first crash of the day involved
Larry Rice on lap 156. With twenty laps to go,
Bobby Unser led his Penske teammate
Rick Mears by a few car lengths.
A. J. Foyt was running third, one lap down. Suddenly on lap 181,
Bobby Unser veered to the inside of the track. He was off the pace with gearbox trouble. That handed the lead to
Rick Mears with 19 laps to go. Less than a lap later,
A. J. Foyt (now in second) got by Mears to un-lap himself. Bobby Unser would stay out on the track and nursed his ailing car to a 5th-place finish in third gear.
Finish Rick Mears made his final pit stop from the lead on lap 185. He took on fuel only, and no tires.
A. J. Foyt followed, completing a fast 8.5-second pit stop. The leaders pits stops were over, and Mears now held a 38-second lead over Foyt. Suddenly with 8 laps to go,
Tom Sneva wrecked in turn four, bringing out the yellow, and bunching up the field. The green came back out for one last sprint to the finish with four laps to go. Rick Mears led, with A. J. Foyt at the tail-end of the pack.
Mike Mosley was one lap down in third place, however, an early-race scoring error was tentatively showing him two laps down in 5th place. Foyt was mired in heavy traffic, and needed to pass at least 14 cars to catch up to Mears. With Foyt struggling to make up the ground, his engine lost a cylinder. Down on power, Foyt began to slow. Third-place
Mosley, fighting to stay ahead of fourth-place Danny Ongais, un-lapped himself on the final lap and continued to charge. Meanwhile, Mears cruised unchallenged to the finish line. Mears in only his second start, won his first of four Indy 500 victories. Coming off of turn four with the checkered flag waving, A. J. Foyt's engine quit. He pulled to the inside and was coasting down the frontstretch towards the finish line.
Mike Mosley was storming down the frontstretch at full speed, but Foyt nipped him at the finish line by 2.3 seconds to hold on to second position. Though it was not known at the moment, Mosley's charge on the final lap nearly gave him second place. After the race, officials discovered a scoring error, and realized that Mosely was not credited with a lap at the start of the race. In the official results, Mosely was credited with third place, just behind Foyt.
Bill Vukovich II, who was one of only two drivers to make the field during the special Saturday qualifying session, charged all the way from 34th starting position to 8th at the finish. Born in 1951,
Rick Mears became the first Indy 500 winner born after
World War II. It was also the last checkered flag for
USAC chief starter/flagman Pat Vidan. This would be the final Indianapolis 500 participation for
Team McLaren who left Indy car racing as a team all together until their return in
2017. ==Box score==