If you watched the 100th running of the Indianapolis 500 on Sunday, you saw some incredible see-sawing at the front of the field all day, but the most insane part of the race was former Formula 1 driver and American rookie Alexander Rossi suddenly appearing in the race lead with four laps remaining and holding on to win. Rossi, running for the small Bryan Herta Autosport now paired with Andretti Autosport, had clearly saved fuel where others had not and when the race leaders had to stop for a splash, there was Rossi, lugging his Honda behind lapped Andretti teammate Ryan Hunter-Reay to the checkered flag and running out of gas on the back straight at Indianapolis Motor Speedway. It was maybe the most improbable outcome because nobody had been paying attention to Rossi in the lead-up to the final dash. When it was all said and done, Rossi seemed at a loss to explain what had happened, but his race engineer had clearly pulled a fast one on everybody. It’s still hard to grasp, but let’s see if we can unravel the mystery a bit.

Almost the entire field pitted under caution on Lap 165, which theoretically put all the lead-lap runners on equal footing. J.R. Hildebrand stayed out knowing he’d need to take service, but his race engineers at Ed Carpenter Racing were gambling on everyone else coming up short. This made sense because a typical green-flag fuel run was about 31 laps. If the race stayed green until the end on Lap 200, it was going to be extremely difficult for anybody to save enough fuel to stretch that 31 laps to 35 (with a couple of caution laps before the restart on Lap 167). That ultimately didn’t pay off the way that Hildebrand had hoped, but the one-off driver was happy with a Top 10 finish as a result.

For the frontrunners James Hinchcliffe, Tony Kanaan, Carlos Munoz, and Josef Newgarden, the lowest-risk strategy was to run the cars hard to the end and hope for at least five or six laps of caution or for everyone else to require a splash of fuel also. It nearly worked and for the sake of the explanation, we’ll only look at Munoz and Newgarden by the numbers since they finished on the podium.

Further back on the restart, however, some teams might find it worthwhile to try stretching fuel to the absolute limit in anticipation of the leaders running themselves out of gas first. To do it right, however, the driver would have the unenviable task of saving fuel while also running a pace that wouldn’t put him so far back that the hard-running leaders could still pit for fuel and come out ahead. And to make it work, they would have to do it from the second they left the pit box the final time. Endurance racing fans will know this is challenging even on a road course with multiple braking zones and the ability to carry speed in different ways, but on an oval? That’s a world-class challenge.

Still with me? OK, here’s where things get interesting.

At least three drivers tried to make it work. Obviously, Rossi was one of them, but Chip Ganassi Racing driver Scott Dixon and Charlie Kimball both gave it a go. On the restart, Dixon started 6th, Rossi 9th, and Kimball 12th. Dixon and Rossi essentially kept pace together and for 17 laps with Rossi just behind Dixon. It’s worth noting here that Dixon has developed a much-deserved reputation as one of the best in the world at saving fuel without losing pace, a fact that lends even more gravitas to Rossi outfoxing one of the world’s best at his own game.

The pair moved up a few places, settling into 5th and 6th with a bit of distance to the frontrunners. However, Ganassi’s engineers ultimately decided that the plan was just not going to be enough and they pre-empted the fuel-savings run by bringing Dixon in on Lap 191, which would let him at least run full-rich to the end.

Kimball meanwhile ensured he was saving enough to fuel to get to the end, but he wasn’t running nearly the pace that Rossi was. And unlike Dixon and Rossi, he wasn’t moving forward in the field enough to clear Munoz and Newgarden with their respective fuel stops. By the time teams were making decisions about whether a yellow flag would come out—probably around Lap 190—Rossi had more or less invisibly sealed the fate of the race.

Here’s how the laps from the restart until Lap 190 compared. It’s interesting that Dixon and Rossi were running the same pace, essentially, but Dixon’s engineer didn’t figure they’d have enough fuel. Maybe it was because Dixon was running in clean air without the fuel-economy benefit of the draft, maybe they didn’t think that a final-lap speed of 178 mph like Rossi made was going to be enough to clinch the win.

And here’s how those 35 laps of the race look when each driver’s laps (in mph) are overlaid. Newgarden and Munoz clearly pushed hard and were the fastest cars, but contrary to popular belief, the fastest car doesn’t always win as a gutted Carlos Munoz found out the hard way. Kimball ultimately did make it to the end of the race thanks to a huge dip in pace right after his teammate Dixon pitted. Rossi, however, waited until he’d cleared Munoz by a half-lap before letting off the pace. Until those final four laps, Rossi had been an incredible picture of consistency.

And here’s one more plot showing the race positions in the closing minutes. It’s easier to see here the direct results of Rossi’s steadiness; he was simply a machine moving forward in the field methodically until Newgarden and Munoz had to take their splashes of fuel. Then he was winning and 350,000 people at Indianapolis Motor Speedway lost their minds. Kimball’s super-slow laps ultimately cost him too much valuable track position, dropping him all the way back to 13th with just 13 laps to go. At that point, he’d gone backward far enough that he couldn’t go all the way to the front, although a fifth-place finish is pretty darned good from a car that had scarcely seen the Top 10 for most of the race.

OK, so that’s an awfully long way to go to explain how the race played out, but the staggering shock of Alexander Rossi emerging from almost nowhere to win the Indy 500 in just his second-ever oval race…well, that’s the kind of drama I suppose we predicted for the grandiose 100th running. A good writing teacher once told me “A good ending is a surprise that makes perfect sense in retrospect once you go back and inspect the elements.” And whoever scripted this Indy 500 twisted the plot into knots.