Sometimes you just have to say: “Too good,’’ which is effectively what former Olympic champions Kyle Chalmers and Zac Stubblety-Cook did after finishing with silver medals in events they hoped to win at Paris 2024. In both cases, Australia’s contenders bowed to new generation talents.

China’s Pan Zhanle put together the most extraordinary 100m freestyle in the history of the sport to take 0.4 of a second off his own world record, setting the other-worldly time of 46.40sec. He is now almost half a second quicker than the next fastest man in history, an unthinkable margin in the blue riband sprint.

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The 2016 champion Chalmers always insisted that if he was in the race, he would back himself, and he did defeat those operating on the previous level of the event, touching out former world champion David Popovici for the silver in 47.48sec. The 26-year-old Australian produced his best race of the year, but he would have needed a time-shift to get on terms with the Chinese swimmer in this race.

In the modern era, since the standardisation of the 50m pool in 1954, no-one has won the men’s 100m freestyle by more than a second, not even close. The margin was so great that the ever-competitive Chalmers could find nothing with which to reproach himself.

“I think I did the very best I possibly could do and it’s a season best time for me… [I’m proud] to be able to deliver in the big moment with all the pressure and expectation and the crowd going crazy,’’ Chalmers said.

Like the rest of the crowd, he was left open-mouthed as Pan surged through two laps in a time that Chalmers said he had never imagined seeing on the scoreboard at the end of a race.

“It’s crazy,’’ Chalmers said. “I did everything I possibly could to execute an amazing race and in the last 15 metres, breathing towards him, I thought I could be dead last because he was so far ahead of me.”

“For him to produce a 46.4 and break the world record in the Olympic final is incredible compared to yesterday going 48.4 in the heat and almost missing [the semi-final]. It’s great that he’s able to reset and refocus and swim so fast.”

There will inevitably be speculation about such an exceptional performance, in the wake of doping allegations surrounding the 23 Chinese swimmers who tested positive to a banned substance before the Tokyo Games. Chalmers was not prepared to feed that suspicion.

“I do everything I possibly can to win the race and I trust that everyone’s doing the same as I am and staying true to sport and the integrity of sport,” Chalmers said. “So yeah, I trust it, I trust that he’s done everything he possibly can to be there and he deserves that gold medal.’’

Chalmers is now one of a very select group of three men to have won three consecutive 100m freestyle medals, his gold-silver-silver sitting just beneath Alex Popov and Duke Kahanamoku’s gold-gold-silver.

The 2016 Olympic champion said he was particularly proud of his longevity and his ability to overcome setbacks in a nine-year international career. He declared that he intended to swim on for the Los Angeles Games in 2028 but accepted that would require him to open his mind as to what was possible in the 100m freestyle.

“46.4 is amazing, it’s a time that I probably never dreamed or saw as possible,’’ Chalmers said. “I’ve got to start setting myself that goal of being 46, for me to be competitive and stay competitive.’’

Just one year ago, before the world championships final in Fukuoka, Pan approached Chalmers and told him that he was “his idol”. That day Chalmers won the world title in 47.15sec and Pan was fourth in 47.43. In less than a year, the 20-year-old Pan has found more than a second to redefine the event.

Stubblety-Cook was also at peace with his performance after adding silver to his gold in Tokyo. Well before the 200m breaststroke final, Australia’s defending champion knew what he was in for.

Asked if France’s new hero Leon Marchand was a threat in this event, despite having to back up from the 200m butterfly final an hour earlier, Stubblety-Cook didn’t hesitate.

“Absolutely,’’ he said. “It’s pretty simple. He trains with Bob [Bowman, the architect of Michael Phelps’ unparalleled career] so he’s got a big engine behind him.’’

Related: Léon Marchand seals historic double with gold in 200m butterfly and breaststroke

In the end, that big engine ran Stubblety-Cook down. The Australian came into the Games searching for his best form and he almost found it, clocking 2:06.79, just a touch slower than his winning time in Tokyo (2:06.38). But it was not enough to withstand Marchand’s momentum, as he claimed his second gold medal of the night. The Frenchman secured his third gold medal of the Games in an Olympic record of 2:05.85, the second fastest time in history.

“I was stoked with that result,’’ Stubblety-Cook said. “To be back at 2:06 is awesome and Leon is like the ultimate competitor, so for me, I was absolutely stoked. I left nothing out there. To see Leon go a 2:05.8, I can’t complain because it’s better than my best.”

Stubblety-Cook made his usual late charge down the last lap, and recovered considerable ground on his rival, but the lead was too great. “Give me another 20 metres, I might have had it,’’ he joked. But with the French crowd baying for Marchand, there was a sense of destiny about the Frenchman last night.