Nyree Kindred set a new Paralympic record as the swimming programme got under way at the Aquatics Centre.
London 2012 is the 32-year-old's fourth Paralympics and she is looking to add to the nine medals, including two golds, she has already secured.
The Welshwoman was second in the S6 100 metres backstroke in Beijing and she booked her passage into the final in one minute 27.96 seconds, lowering by 0.22secs the mark set by China's Lu Dong in the first heat.
Kindred, who was the first Briton into the pool, said: "I couldn't ask for anything better in a heat swim.
"I would like to go quicker; that was a hard race so I am going to try with the crowd with me.
"But anything could happen because all those girls who made that final are capable of a lot more so you've just got to watch this space and see what happens."
Chants of 'Team GB' - here the team is actually called ParalympicsGB - had reverberated around the 17,500-capacity venue before Kindred's race with noticeably fewer empty seats than at the Olympics.
She said: "It's uplifting. It does spur you on because at previous Games it's really been about the other athletes, like for the Chinese in Beijing.
"Here you know they are cheering for you, they are not trying to intimidate you or make you nervous, they are trying to lift you and get you going.
"It worked and I was just trying to focus and make sure I could listen to the starter as well."