As the medal tally rose Scot Gordon Reid kept himself in the running for two medals after making it through to the quarter-finals of the doubles wheelchair tennis.
It was another thrilling day at the aquatics centre with a gold performance from Simmonds.
The swimmer smashed her world record to win a second gold medal last night – declaring "I'm just so chuffed."
Just 48 hours after winning her first gold, the teenager came first in the 200m individual medley.
This time there were no tears, just a trademark beaming smile. The 17-year-old said: "I'm just so pleased – another world record.
"I'm so chuffed."
It was a case of double delight for Team GB, as compatriot Natalie Jones won bronze.
Jones, 27, who has cerebral palsy, said: "I'm delighted to have a medal and can't believe it was so flippin' close."
Simmonds broke her own world record – which she set in the qualifiers – to take gold number two.
The win – which comes just two days after winning gold in the 400m freestyle –makes her the third paralympian to taste double gold success alongside cyclist Sarah Storey and equestrian Natasha Baker.
The race was attended by Prime Minister David Cameron, who cheered on our Paralympic heroes.
Mr Cameron kissed Simmonds and shook her hand as he presented her with the gold medal.
Today Simmonds, who has dwarfism, will be hoping to make it a hat-trick of golds as she races in the 50m freestyle.
Helensburgh's wheelchair tennis star Reid progressed to the next stage with his partner Marc McCarroll as he chases a Paralympic medals double.
He has also reached the third round of the singles competition at Eton Manor.
The 21-year-old and McCarroll, who are seeded seventh, yesterday beat Belgium pair Mike Denayer and Joachim Gerard to set up a meeting with fourth seeds Frederic Cattaneo and Nicolas Peifer of France.
Reid, who is seeded ninth in the singles, will play Sweden's sixth seed Stefan Olsson for the chance to reach his second quarter-finals of the Games.
"It's not difficult at all to balance the singles and doubles," said Reid. "Both are equally as important to me. I know I have a chance so I'm just giving my everything in both.
"The crowd was going absolutely mental for us at every point."
Elsewhere, there was disappointment for equestrian star Lee Pearson, who won bronze at Greenwich Park.
Had he won the Grade Ib freestyle competition, the 38-year-old, from Staffordshire, would have joined Tanni Grey-Thompson and swimmer David Roberts with 11 Paralympic golds.
Meanwhile, Nigel Murray's GB mixed boccia team saw their chances of retaining Paralympic gold extinguished – although they could still win bronze.
The quartet started the day well by overcoming Hong Kong 11-3 in the quarter-finals, but they struggled when play recommenced yesterday afternoon.
Great Britain were no match for a dominant Thailand team ranked second in the world, going down 18-1 in the semi-final.
Organisers hailed the "superb" start to the Games, which has now seen 101 Paralympic records set in front of packed stadiums.
Team GB is well ahead of schedule in its quest for 103 medals, with 63 – including 19 golds – after five days.
ParalympicsGB chef de mission Craig Hunter hailed the "superb start", adding that the athletes are "slightly ahead of our Beijing total (at this point in 2008)".
Channel 4 announced the highest ever TV Paralympics audience for Oscar Pistorius' defeat in Sunday night's T44 200m final.
Almost 4.5 million tuned in to watch the 25-year-old South African double amputee lose his 200m crown to Brazilian Alan Oliveira.