British 400m hurdler Dai Greene sneaked into the London 2012 Olympic final after making it through as one of two fastest losers on Saturday.
The reigning world champion was beaten into fourth in his semi-final but made it through to Monday's final after a nervous wait.
But his chances of adding Olympic gold to his world title will be hampered by a less than favourable lane draw.
Elsewhere, British duo Rhys Williams and Jack Green failed to advance.
Greene, who was among the favourites for gold, admitted to being shocked at his semi-final performance.
"I was going down the home straight and couldn't catch them," Greene told BBC Sport. "I don't know what happened, I wasn't there. I'm devastated. I'm shocked and feel like I've let everyone down."
Felix Sanchez, the 2004 Olympic champion, 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
Elsewhere on the track on Saturday, GB's Christine Ohuruogu made it through to the final of the women's 400m final after coming second in her semi-final, qualifying seventh fastest.
Ohuruogu, the defending Olympic champion, posted a time of 50.22 secs, as she looks to defend her title on Sunday (21:00 BST).
But fellow Britons Shana Cox and Lee McConnell failed to advance.