Adam Gemili became only the second British man to run under 20 seconds for the 200m in qualifying for Saturday's World Championships final.
The 19-year-old clocked 19.98, the second fastest time in the semi-finals, before declaring himself "speechless".
John Regis, whose British record stands at 19.87, is the only Briton to complete the distance in a faster time.
Defending champion Usain Bolt won his semi in a time of 20.12, while American Curtis Mitchell won his in 19.97.
James Ellington finished fourth behind Bolt in a time of 20.44 and fellow Briton Delano Williams was seventh behind Mitchell in 20.61.
Gemili, the 100m European Under-23 champion, put his hands on his head in disbelief as he learned he had dipped a fraction ahead of Jamaica's Nickel Ashmeade.
"I can't believe it. Honestly, that's the best feeling in the world," said the Blackheath and Bromley Harrier, who competes in Saturday's final at 17:10 BST.
"I didn't realise it was me, I didn't know if I'd qualified. I've made the final and I've run a personal best. I'm so grateful to so many people.
"Whatever happens now, I've put myself among the greatest 200m runners in the world and I can't ask for more than that."
One of the greats Gemili was talking about was Jamaica's Bolt, who will be bidding for a third consecutive 200m world title.
The Olympic champion strolled into the final and will be favourite to retain his title despite Mitchell, Gemili and Ashmeade (20.00) running quicker than him in the semi-finals.
"I started taking it easy," admitted Bolt, who won the 100m title in Moscow on Sunday.
"I tried to pace myself and in the last minute I heard footsteps behind me so I had to change gears a little bit. I'm feeling alright and I've just got to get it done."
Gemili's team-mate Chris O'Hare, 22, produced another surprise performance by qualifying for the 1500m final with a comfortable fourth-placed finish in his heat.
However, both Marilyn Okoro, 28, and Laura Muir, 20, failed to qualify for the women's 800m final. The pair finished seventh in their respective races.
Elsewhere, the British quartet of Eilidh Child, Shana Cox, Margaret Adeoye and individual 400m champion Christine Ohuruogu qualified fourth fastest for Saturday's 4x400m final after winning their heat in 3:25.39.
However, without the injured Perri Shakes-Drayton, who returned to the UK on Friday for treatment on her knee, the GB team will face a difficult task to get past the US, Russia and Jamaica in the final to win a medal.