Ellie Simmonds claimed ParalympicsGB's second gold medal in the pool of London 2012 when she triumphed in her S6 400 metres freestyle shoot-out against Victoria Arlen and demolished the American's world record by more than five seconds.
Victory in five minutes 19.17 seconds followed the gold won by Jonathan Fox on the opening night and came immediately after Simmonds' Swansea team-mate Matthew Whorwood secured bronze in the previous race in the men's equivalent.
The crowd at the Aquatics Centre had grown increasingly more raucous as Whorwood made his way to the bronze in the previous race and on Simmonds' introduction the noise was intense.
The pair were neck and neck going into the final turn with the Briton 0.08 secs ahead and as she pulled away, the American had no answer as Simmonds touched first to send the crowd into a frenzy.
It was only at 2pm that Arlen's participation in the race was confirmed in a statement released by the International Paralympic Committee.
Earlier this week the American swimmer had been deemed ineligible for competition and excluded from London 2012.
The United States' appeal to the IPC was upheld and the 17-year-old was reinstated on Thursday.
In a two-stage process, Arlen passed an initial assessment but she was also observed during racing and it was only following the heat that any doubt surrounding her involvement in her three S6 freestyle events was dispelled with a review in a year's time.
A swimmer's classification can change for different strokes because the nature of their impairment may affect their ability to perform a particular stroke. This applies to Arlen who competes in the SB5 class in breaststroke in which she will continue to be observed.