London - Usain Bolt's bid to bring the curtain down on his glittering career with a 15th world gold medal remained on track as Jamaica qualified for the final of the 4x100m relay.
Bolt took the unusual step of racing the relay heats, something usually reserved for the more unheralded members of the squad.
Tyquendo Tracey, Julian Forte and Michael Campbell safely negotiated the first three legs before Bolt steered his team home in a winning, season's best of 37.95 seconds.
"It's been brilliant. The energy in the stadium is outstanding," Bolt said, hailing the deafening support in the packed-out London Stadium "not just for me but the whole championships".
Bolt said his emotions were still in check at the thought of bowing out of track and field.
"For me it's hard to be sad because the energy I'm getting from the crowd is brilliant, I'm just happy."
Bolt's bid to retain his 100m title went up in smoke as American Justin Gatlin won gold, with Christian Coleman taking silver.
It was the first time Bolt had been beaten at a major championships since the 4x100m relay at the 2007 worlds in Osaka.
The 100 and 200m world record holder, who also anchored the Jamaican squad to a world record in the relay of 36.84sec at the 2012 London Olympics, will be back at the track for the final at 2050 GMT.
Bolt has amassed eight Olympic golds and 14 world medals, 11 of which are gold, the Jamaican having won two silvers in 2007 before his 100m bronze in London.
No matter the result of the relay, organisers said Bolt will be afforded a dedicated lap of honour on Sunday in tribute to his amazing track career.
Gatlin ran the second leg for the US team, led off by Mike Rodgers, another dope cheat, BeeJay Lee and Coleman on anchor.
They clocked 37.70 seconds to finish 0.06sec ahead of Britain.
Also qualifying for the final were France, China, Japan, Turkey and Canada.