The 21-year-old comfortably made his way through to the 5.91m mark in Brussels, at which point he dispatched of his remaining two competitors, but needed all three attempts to clear 6.05m.
At that point he decided to go for 6.19m - 4cm above his world record and 1cm higher than his indoor world record - but was unable to achieve the feat, and will now head to next week's final in Zurich in pole position to win the 2021 title.
Team GB's Dina Asher-Smith was back in action in the 200m following hamstring heartbreak in Tokyo, finishing third with a new season-best of 22.04 seconds as Namibia's Christine Mboma won a Diamond League event for the first time in her career.
The final meet of the season takes place next Wednesday and Thursday in Zurich. body check tags ::