Usain Bolt, in his final ever race, pulled up with what appeared to be a hamstring injury having received the baton for the final leg.
A distraught Bolt was consoled on the ground by his sprint team-mates and he limped out of the stadium, not the way he probably envisaged his send-off going.
More booing too for 100m gold medal victor Justin Gatlin on his entry, who ran the second leg with the American team along with Mike Rodgers, Jaylen Bacon and Christian Coleman, who won the individual gold. Expect Jamaica and U.S. to fight for golds should they get the baton round, while Germany have strong teams and Britain have high hopes of snatching a life-affirming fourth.
Bolt, who is the greatest sprinter in modern times, has been chalked fame and fortune. Mitchell-Blake was in tears and could barely speak.
Running the second leg, Allyson Felix and her teammates crossed first in a season's leading time of 41.84 seconds, beating Britain and Switzerland.
The winning time, a combination of Ujah's ideal reactions, flawless changeovers and a superbly-timed dip from Mitchell-Blake to cross the line ahead of 100m silver medallist Christian Coleman, erased the 18-year-old European record of 37.73 - also held by Britain.
China, silver medalist two years ago, was fourth in 38.34.
"He kept apologising to us but we told him there was no need to apologise", Forte said. "This is just so incredible to be a world champion again".
"I wasn't sure if I had won or not, I gave it my all but I could see Christian Coleman out of the corner of my eye", said Mitchell-Blake. It's a massive team effort and we win as a team and lose as a team.
Hours later, Bolt took to Twitter to thank those who wished him well after the injury.
The four - the same line-up who won Team GB's first 4x100m relay bronze in 32 years in Rio last summer - crossed the line 0.09 seconds behind the United States of America, with Germany qualifying as third fastest.
In the opening heat, Spain beat Poland and Cuba for the three automatic qualifying spots but Jamaica was out, finishing fourth. "We know what we can do and we'll be ready in 2019", he added.
Lasitskene, who missed last year's Rio Olympics because of Russia's suspension, failed at 1.99 twice but regained form thereafter.