Two days after setting a world record of 9.58 seconds to win the 100, the Olympic 200 champion ran a good curve and coasted through the final straight to finish in 20.41 seconds, a full 1.11 seconds behind his world record.
In the absence of injured defending champion Gay, Bolt is the overwhelming favourite for gold, and he said he would try to get a second world record at the championships, too.
The Jamaican set a record of 19.30 seconds at the Beijing Olympics, widely considered one of the toughest to beat in the sport.
The U.S. team needs to change something quick to challenge the Jamaicans for sprint supremacy at the championships. They lost 5-0 in Olympic titles at the Beijing Games and are already 2-0 behind after the 100s. The specter of another rout is looming ever larger, especially with Gay out for the 200 and doubtful for the relays.
The final for the 200 is set for Thursday. Bolt is also favoured to lead Jamaica to a sprint relay gold on Saturday to equal his feat of three golds at the Olympics.
If the loss of Ohuruogu was a setback for Britain, Phillips Idowu made up for it, winning the triple jump ahead of Olympic champion Nelson Evora of Portugal.
Idowu, the runner-up at last year's Beijing Olympics, jumped 17.73 meters - the best of the season - while Evora could muster no better than 17.55.
The host nation won its first gold when Steffi Nerius won the javelin ahead of favorite Barbora Spotakova of the Czech Republic.
Kenya continued its domination of the steeplechase. Ezekiel Kemboi, the 2004 Olympic champion, won ahead of Richard Mateelong and set a championship record of 8:00.43. Bouabdellah Tahri of France settled for the bronze but set a European record.
