The Aquatics Centre breathed a huge sigh of relief as Olympic champion Rebecca Adlington squeezed into the final of the 400 metres freestyle in eighth place.
The 23-year-old swimmer dominated her race from start to finish but then had to look on as two extremely fast heats threatened to edge her out of Sunday night's final.
However, her time of four minutes 05.75 seconds just saw Adlington through although the event has such strength in depth that making the podium will be a battle royale, let alone successfully defending her title.
World record holder and world champion Federica Pellegrini was herself only seventh with Frenchwoman Camille Muffat, the textile world record holder who has been on startlingly consistent form this year, quickest in four minutes 03.29 seconds.
Before she realised she had just squeaked through, Adlington said: "It felt faster than that but you just don't know being in the first heat. I had no option, I just had to go for it. I hope it's enough to make the final."
Beijing bronze medallist Jo Jackson was 21st in 4mins 11.50secs.
In Adlington's case, it was reminiscent of Michael Phelps on Saturday when the 14-time Olympic champion just edged into the 400m individual medley final.
Mansfield-born Adlington will be hoping for a better outcome to her final than Phelps experienced after he was locked out of the medals in fourth place.
She can draw confidence from previous experience having claimed the silver medal at last year's World Championships in Shanghai despite swimming from lane one after finishing seventh in the heats.
Similarly, at the previous World Championships in Rome she won bronze also from an outside lane, so in that respect she has nothing to fear.