The instant that Noah Lyles crossed the finish line in Sunday night’s heart-stopping 100-meter final at the 2024 Summer Olympics, the clock started on a completely different sort of race.

With the American sprinter and his rivals bunched so tightly at the end, it was impossible to divine a winner with the naked eye.

So, far above the track, a team of officials immediately turned to their computer screens and got to work determining an order of finish.

2024 Paris Summer Olympic Games

“All of this happens, obviously, very fast,” said Alain Zobrist of Omega, the Swiss company contracted to keep time at the Games. “There is a lot of pressure.”

The photo finish process begins with three cameras — main, backup and infield — aimed at the track from different angles. Officials need multiple views in case one runner is partially blocking another.

The cameras take 40,000 pictures per second, beaming the images to a temporary, three-level structure built into the stands at Stade de France. Zobrist calls them “the quietest rooms in the stadium. Everyone is extremely focused.”

On one level, a main timekeeper, head judge and team leader scrutinize footage from the main camera. On another level, an official studies the infield and backup perspectives.

Using the left and right arrows on their keyboards, they can scroll back-and-forth between images, zooming in and out where necessary. The pictures highlight a critical area within five millimeters of the finish, but humans must decide.

“The head judge is making the call and everyone else is confirming,” Zobrist said.

On Sunday night, that meant looking past the jumble of feet, hands and heads because, under international track rules, a runner does not finish until his or her torso crosses the line.

Timekeepers say they found a clear view for the 100 and checked below each image for an exact time down to the thousandths of a second. Then they paused to confirm their finding. Zobrist explained: “As soon as you officialize, there is no way back.”

Seconds ticked by — about 10 of them — as runners on the track and thousands of spectators in the stands watched the stadium’s video boards. Lyles did not expect his name to be atop the list.

“I wasn’t ready to see it,” he recalled. “And that’s the first time I’ve ever said that in my head, like I wasn’t ready to see it.”

Noah Lyles celebrates after winning gold in the men’s 100 meters Sunday at the Paris Olympics.

(Wally Skalij / Los Angeles Times)

A roar filled the stadium as photo finish results flashed across the screen. Lyles had edged out Kishane Thompson of Jamaica, 9.784 seconds to 9.789. Another U.S. sprinter, Fred Kerley, finished third just .02 back.

Still, officials were not done. On the third level of their temporary facility, they used motion sensors and a positioning system to better understand what had transpired on the track.

With a reaction of .178 seconds, Lyles started relatively slowly out of the blocks. But he reached 26.7 miles per hour at about 65 meters and unlike Thompson, who decelerated toward the end, was able to more or less maintain his peak speed. This allowed him to take the lead at about nine seconds and lean for the line.

The entire race took slightly less time than figuring out who won it.