They won in 37.47 seconds, with the U.S. taking silver at 0.05sec and Japan with a surprise bronze.
"It was ridiculous. We were there around 45 minutes waiting outside, I think they had three medal ceremonies before we went out so we were really trying our hardest to stay warm and keep upbeat". He ran his last individual race, the 100m, last Saturday, managing only a bronze; no fairytale finish for him.
"Usain was getting cold and he said "I don't like this".
"He didn't tell us exactly what happened but from what I saw, it looked like a strain or a cramp of some sort", teammate Julian Forte told IAAF radio.
"The 10k did take a lot out of me and I'm a little beaten up, but I'm OK", Farah said.
The Briton is aiming to complete an unprecedented World Championship triple-double, having retained his 10,000m title on the first day - the home nation's only medal. "We hope for the best for him".
Briton Farah, 34, will retire from the track this month to concentrate on marathons, while Jamaican legend Bolt's last event will be the 4x100m relay.
Jamaica were afforded a rousing welcome from the crowd, a relaxed-looking Bolt applauding the stands, with pictures of him constantly shown on the stadium's big screens.
"It's heart-wrenching", said McLeod, who is also the Olympic champion.
"I drank like two bottles of water".
Britain's 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, was a new national record, erasing the 18-year-old mark of 37.73. It felt like it was there but the reason I lost because I couldn't get it. "He is still the best in the world", Gatlin said.
"I think they were holding us too long in the call room". He was running out there cold.
However, Blake - who missed out on a medal in the 100m, failed to make the 200m final and was an injury doubt in the hours leading up to the race - was overtaken around the bench by Jaylen Bacon and Daniel Talbot.