Heather Frederiksen secured her first gold medal of London 2012 when she successfully defended her title in the S8 100 metres backstroke.
Frederiksen qualified comfortably fastest in the heats and she was ahead at the turn.
It looked as though she would be attacked down the final length but she dug in and easily held off Jessica Long of the United States and Olesya Vladykina of Russia to win in one minute 17.00 seconds.
The 26-year-old has battled ill health over the past year which has seen her hospitalised or often bed-ridden, and she came into London after just six weeks' training.
Frederiksen told Channel 4: "I'm so pleased. I really really wanted that today, more than anyone ever knows, and I wasn't going to let that go. I was so hungry for it.
"I turned at 50 and thought I've just got to keep it going - the crowd got me home. I've raced Jess a few times this year. I knew what I had to do and I've done it."
Earlier, Oliver Hynd got Great Britain off to a good start when he claimed the first medal of the night with bronze in the S8 100 metres backstroke at the Aquatics Centre.
The 17-year-old qualified third for the final and he was in that position pretty much from start to finish.
He touched in one minute 08.35 seconds to secure his second medal of the meet after his silver in the S8 400m freestyle.
Team-mates Thomas Young and Sean Fraser were fourth and fifth after they replicated exactly their qualification positions from the morning's heats.