Caeleb Dressel, 24, who represents Cali Condors in the ISL, swam 100 butterfly in 47.78.
Thus, he was 67 hundredths faster than the second Chad le Clos.
Le Clos also had the previous world record of 48.08 and thus Dressel was the first to swim the distance in under 48 seconds.
In the 50 meter freestyle, Dressel already had the world record, but now lowered it to 20.16.
The world record gives twenty extra points to Cali Condors in the final.
Four teams are in the final of the ISL.
It will be decided tomorrow.