The Kiwi has made a stunning start to his Olympic campaign, swimming an almost perfect heat to qualify for the 400m Individual Medley final.
Clareburt, who is regarded as New Zealand's best podium prospect since Lauren Boyle, stopped the clock at 4:09:49, to beat a strong field home in the third heat.
The 22-year-old rose to the occasion, managing a personal best and setting a national record.
Competing at his first Olympics, Clareburt showed no sign of nerves, with a textbook performance, earning high praise from the poolside commentators.
"Our friends from New Zealand are right, they've uncovered a gem in Lewis Clareburt."
With the top eight qualifying for the final, he swam the second best time of the night, only behind Australian Brendan Smith (4:09:27).
In a major shock, the pre-Games favourite and Japanese hope Seto Daiya will miss the final, after placing fifth in the last heat.
In lane three, Clareburt was placed second after the butterfly leg, before accelerating in the backstroke section, to lead the field by 1:28 seconds. Clareburt dropped to third during the breaststroke, before a powerful freestyle leg.
Five swimmers were on the charge on the final lap, but the Kiwi was good enough to edge ahead of the pack.
Clareburt finished 0.16 seconds ahead of American Chase Kalisz, with David Verraszto (Hungary) 0.31 behind the Kiwi. Kalisz won the silver medal in Rio.
Clareburt's previous personal best, set earlier this year, was 4:09:87.
It's a cut-throat scenario in this event – with no semifinal stage – so there was only one chance to impress and make the final.
Afterwards Clareburt rated his performance at just 2 out of 10 and said had a lot more in the tank for the final.
"I was happy with that," he said. "I thought I went out a bit slow, but I stuck to it in the breaststroke and then had enough to come back at those guys in the freestyle. It's nice to get the first race over and done with."
The Wellingtonian first caught the eye at the 2018 Commonwealth Games on the Gold Coast with a bronze medal. While some sports are considerably weaker at Commonwealth level, it's not the case in the pool, with the presence of the all-powerful Australians as well as the English.
His standing was confirmed at the 2019 World Championships in South Korea, with a stunning podium finish, just the fifth Kiwi to medal at that level.
Zac Reid couldn't emulate Clareburt's achievements, finishing sixth in his heat to miss qualifying for the 400 metre freestyle final.
The New Plymouth swimmer recorded 3:49:85, just over four seconds behind the winner Antonio Djakovic (Switzerland).
The 21-year-old started well, placed second after the first quarter of the race. But he couldn't maintain the pace, gradually slipping back.
His time was outside his personal best of 3:47:74.
Reid gets another chance in the 800 metre freestyle event on Tuesday.
