In intermittent, stormy rain, Duplantis cleared 6.02m on the first try, before failing at 6.10m.
His best jump of the summer season so far was a bar placed at 6.01 m.
Earlier in the competition, the young Swede (22) had a scare by only passing 5.92m on his last attempt.
The American Sam Kendricks, who was to start his international season on the Norwegian jumper, gave up on him at the last minute, a sore knee.
If his qualification for the World Championships in Eugene (United States) in a month (July 15-24) is assured by virtue of his status as (double) reigning world champion (2017 and 2019), his form necessarily questions .
It is a priori expected in Paris in 48 hours.
Renaud Lavillenie capped him at 5.60 m, his entry bar into the competition, crossed on his second try.
After a stalemate at 5.70m, the 2012 Olympic champion failed three times afterwards, once at 5.80m and twice at 5.86m.
His little brother Valentin did not pass any bar: he knocked down the one set at 5.40 m three times.
Duplantis won ahead of two Norwegian pole vaulters, Sondre Guttormsen and Pal Haugen Lillefosse, who both stayed at 5.80m.
The outdoor world gold is the only one missing from his charts.
© 2022 AFP