Team captain Dai Green scraped into the Olympic final of the 400 metres hurdles in a dramatic start to an evening which was expected to bring Britain's first athletics medals.
World champion Greene lay on the track with his head in his hands after crossing the line fourth in the opening semi-final, with only the first two qualifying automatically and the next fastest two from all three semis also reaching Monday's final.
That meant an anxious wait for the 26-year-old Welshman to see if his time of 48.19 seconds would be good enough - a wait which ended when a massive roar from the 80,000-strong crowd confirmed he had enjoyed a lucky escape.
However, there was bad news for Greene's training partner Jack Green, who clattered into the third hurdle in the second semi-final and crashed to the track.
The 20-year-old looked to have suffered an injury in the fall but was fit enough to get to his feet, pick up the offending barrier and slam it into the track.
European champion Rhys Williams also missed out after finishing fourth in the last semi-final in 49.63 secs, while 2004 Olympic champion Felix Sanchez was the fastest qualifier in 47.76 - the quickest time in the world this year - ahead of previous world number one Javier Culson, who clocked 47.93.
Speaking before he knew he had made the final, Greene said: "I can't believe it. I'm just devastated. I went off at a decent pace. I couldn't believe I wasn't closing them down (in the final straight). I'm just shocked."
Green had tears in his eyes as he said: "It's a lack of experience in the event. I am absolutely distraught as you can see. I lost my balance, I was already going down and as you can see I now have bloody knees because that track's nice and hard and takes off the skin quite well.
"I am going to have a few rubbish days from now I can tell you that because obviously this isn't the happiest moment of my life so far. I didn't have a great World Championships last year and I came here to do something special and I really had something there, but it obviously doesn't matter now."
Abi Oyepitan, who had reached the 100m semi-finals as a fastest loser, then finished eighth in the first semi in a time of 11.36s, with world champion Carmelita Jeter of the United States winning in 10.83.