Only the German Paul Biedermann, world record holder in 1 min 42.00, and the American legend Michael Phelps (1.42.96) went faster than him over the distance.
Popovici, 17, had already completed the 100-200m double at the Budapest Worlds last June.
Frenchman Yannick Agnel, crowned Olympic champion at the London Games in 2012 with a time of 1.43.14, has dropped to the rank of 4th best performer in history.
In the lead after the start, the Romanian prodigy never let go of first place, and even accelerated in the last 100 meters to easily outstrip the Swiss Antonio Djakovic (1.45.60) and the Austrian Felix Auboeck (1.45.89) .
Popovici improved his personal best by almost three tenths, set at the World Championships in Budapest on June 20 in 1.43.21, the former best world mark in the junior category.
He continues to defy the limits of time, after winning the European title on Saturday in the queen distance of swimming, the 100m, beating the world record held by Brazilian César Cielo, in combination, in 46.86.
© 2022 AFP