The Wolverhampton sprinter came into this event among the favourites for gold but notably struggled at Japan National Stadium, finishing fourth in a time of 44.68 seconds.
The Halifax runner is a medal contender in Tokyo and is even eyeing a new national record, still held by double Olympic champion Seb Coe from 44 years ago.
For a few seconds, it appeared the training partners and roommates here in Tokyo would score Great Britain’s first World Championships one-two in 18 years.