The winner of the men's pole vault event was Kurtis Marschall of Australia, who cleared 5.90m, while Duplantis was forced to settle for silver with a best clearance of 5.80m. Thiery Baptiste of France finished third, also on 5.80m but with more failures.
The result means the Swede's best effort was a whole 51cm lower than his latest world record of 6.31m set in Uppsala in March - the 15th time he has set the world's best vault. It is the first defeat for Mondo since a fourth place at the Monaco Diamond League in July 2023.
The 26-year-old came into another meeting on Swedish soil with ambitions of going even higher, but he looked far from his brilliant best right from the off on Sunday afternoon, failing with his first attempt at 5.60m, a height he will often skip.
He then cleared that height on his second try, and made no mistake with his first attempt at 5.80m, but two failures at 6.00m and one at 6.05m followed, meaning he was out of the competition, and Marschall's third and final attempt at 5.90m was enough for a rare victory over Mondo in front of a stunned crowd.