"Unbelievable feeling", Sato said after he climbed from his auto prepared by the Andretti Autosport team, which Sato joined this season.
Sato became the first Japanese driver to win the Indianapolis 500. This is his first win on an oval and gives Andretti Autosport three of the past four Indy 500s, following Rossi in 2016 and Ryan Hunter-Reay in 2014.
For the second time in four years, Helio Castroneves is the runner-up finisher at Indianapolis.
The 42-year-old led just nine laps but it really felt like he had the right combination of veteran experience and a fast vehicle needed to hold off the field and tie AJ Foty, Al Unser and Rick Mears as four-time Indy 500 champions.
Rookie Ed Jones finished third.
Castroneves, looking for a record-tying fourth Indy 500 win, took the lead with six laps to go from Max Chilton.
Alonso, who was making his IndyCar debut and started the race in fifth position, was running in the top 10 with 21 laps to go in the 200-lap race when his Honda engine suddenly failed.
Paul Gohde heard the sound of race cars early in his life.Growing up in suburban Milwaukee, just north of Wisconsin State Fair Park in the 1950's, Paul had no idea what "that noise" was all about that he heard several times a year.
"I was pointing in the right direction into (Turn) One", said Sato, who was congratulated in victory lane by Franchitti. While the 500 was traditionally won by the fastest and most patient, the DW12 rewarded a driver willing to make two passing moves a lap and do everything in their power to get to the front of the field.
Two-time Formula One champion Fernando Alonso, who bypassed today's F1 Monaco Grand Prix to race in the Indy 500, ran up front all day and led 27 laps before a mechanical failure ended his day after 179 laps.
Then, on Lap 137, one of his closest rivals, Hunter-Reay, suffered a problem that Alonso would have been very familiar with: a blown Honda engine to end his race.
In a race littered with caution flags (and debris), the worst crash was the first.
"Well, when I saw the 77 went into the wall, I knew it would bounce back. I was thinking at that moment that someone from the team was taking a picture because I want that picture at home". Fortunately Dixon was able to walk away from the crash.
What happened after that was more than can properly be explained.
The 42-year-old Castroneves then warmly congratulated Sato and, after noting Sato's age, quipped that "we get better when we get old". "You just hold on and let the safety (do its job)".
Dixon's vehicle then catapulted toward the inside barrier, where it landed and split in half.
"Whether it was the first attempt or eighth attempt or you had a drama in the past, it doesn't really matter", Sato said.
Howard was a lap down when the incident unfolded. Throughout the month, he had looked slow during qualifying, as did the Penske cars but race day brought the best out of the three-time champ. The resulting wreck was nightmarish, with Dixon's Dallara flying into the inside SAFER barrier and landing side-first so violently that the back half of the auto was torn off at the gearbox and thrown back onto the outside of the track.
The other fantastic part of the incident was that Castroneves drove under Dixon's auto while it was in the air. Another Andretti driver, Jack Harvey, crashed.