It came down to a freeze frame, to a numerical measurement basically undetectable, to see which driver crossed the line first Sunday at Kansas Speedway.

And when it was all over, Kyle Larson had edged Chris Buescher by 0.001 seconds in the AdventHealth 400 in the closest finish in NASCAR Cup Series history.

For a moment, Buescher appeared to have pulled off his first victory of the season and the sixth of his career, and his Roush Fenway Keselowski Racing team could be heard on the driver's radio screaming and celebrating. But Larson's crew chief at Hendrick Motorsports was sure it was his driver who had taken the checkered flag, and Cliff Daniels' suspicion turned out to be correct after NASCAR officials analyzed the video in super slow motion.

"That race, from start to finish, was amazing," said Larson of his second Kansas win. "That first stage was incredible. The second stage at the end was fun. The last stage with wrecks, cautions, fuel strategy and tires running long was wild.

"You guys got your money's worth today."

The photo finish was just the culmination of an exciting evening of racing at Kansas after the race had been delayed from its scheduled afternoon start because of rain.

Denny Hamlin seemed to be heading for his fourth victory this season and second in a row as his Joe Gibbs Racing teammate Martin Truex Jr. chased him down after passing Buescher in the closing laps. But a spin by former JGR driver Kyle Busch, who was running fifth, brought out the caution flag with seven laps to go and sent the race to overtime.

After pit stops – where most of the front runners took two tires, except for Truex, who took four – the race restarted with Hamlin and Buescher on the front row. Larson quickly made it three-wide before Buescher emerged with the lead on the white-flag lap. Larson battled back again as Chase Elliott and Truex, who used his four fresh tires to pass multiple drivers, closed in. And by the time the drivers reached the finish line, Elliott had nearly caught Larson and Buescher, who banged off each other to the checkers in the thrilling finish.

The win was the second of the season for Larson, the 2021 Cup Series champion, and the 25th of his career.

NASCAR's timing originally scored Buescher as the victor, but a quick review showed Larson was first to the line. Buescher, however, was not convinced of his runner-up showing after squeezing Larson in Turn 4.

"I sure can't tell in that picture," Buescher said after watching a replay. "We needed that, but we needed a win more. I thought I might have had that one. … I gave him half a lane too much."

Elliott edged Truex for third, while Hamlin, whose four wins at Kansas led all active drivers, faded to fifth.

Contributing: Field Level Media