After victories for Duplantis in the opening two meetings in China in April and May, respectively, pole vault returned to the programme for meeting six of the season, at Oslo's Bislett Stadium.
The Olympic champion began by sailing over 5.62m at the first attempt, before also clearing 5.82m and 5.92m with his first vaults at those heights.
Those three attempts were enough to win him the competition, as only Greece's Emmanouil Karalis cleared 5.82m, before the Greek failed three times with the bar 10cm higher.
Duplantis had two failed attempts when going for the meeting record of 6.03m, but cleared the height with his third and final try, breaking his own record of 6.02m from 2022.
He then extended his winning margin by clearing 6.15m in two goes, before declining to try a greater height.
The world record holder will next compete in front of his home crowd, as Stockholm hosts the next Diamond League meeting this weekend.