Just over a week ago, Bengtström won the Finnkampen at Stockholm's stadium in 49.24, which was a personal record of 0.28 from the Swedish Championships a week earlier.
Tonight's time was a decrease of a huge 0.71.
In three weeks, Bengtström has lowered his personal record by almost a second.
Only Sven Nylanders 47.98 from 1996 and Niklas Wallenlinds 48.35 from 1992 are better than the 21-year-old's time on the Swedish best list.
Bengström's time was equal to the second, Rasmus Mägi, in the A-heat in the Continental Tour gala.
It was won by the Brazilian Olympic third Alison dos Santos at 48.15.
Since the B-final went a couple of minutes before the A-final, Bengtström had the track record for a while.
With his new personal record, Bengtström is sixth in Europe this year.
In the 800 meters, Lovisa Lindh was again in two minutes, finishing third in 1.59.94.
Jamaican Natoya Goule won in 1.58.20.
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Bengtström finished after the win of 400 m Photo: SVT / TT