With silvers for Nyree Kindred and Hannah Russell, the ParalympicsGB Swimming team claimed three medals on day one in the pool.
Having set a world record of one minute 9.86 seconds in qualifying this morning, the Manchester-based Briton took the final out from start to finish.
Ukraine’s S6 European champion Yevheniy Bohodayko, re-classified just days before the Games, came back strongly and put pressure on Fox in the final 25m.
After taking silver in Beijing, Fox wasn’t going to relinquish his lead and he touched for victory in 1:10.46 ahead of Bohodayko (1:11.31) and Croatia’s Mihovil Spanja (1:12.53).
“It’s just an amazing feeling,” said Cornishman Fox. “When you touch the wall and the crowd roars it’s so good.
“It was another good time. I thought I might pip the world record again but I’m so happy to get the gold."
Kindred, who was competing in her fourth Paralympics, struck silver in the S6 100m Backstroke to collect the 10th Paralympic medal of her career.
The world champion missed a year of swimming in 2011 to have a child with husband and fellow British Paralympic swimmer Sascha Kindred.
But having qualified fastest from the heats with a Paralympic record 1:27.96, the Welsh swimmer knew she was back to her best and in the final she clocked a British record 1:26.23 to equal her result from 2000 and 2008.
China’s Lu Dong won the gold in a world record 1:24.71 but Kindred held off defending champion Mirjam de Koning-Peper who claimed bronze in 1:29.04.
Teenager Russell won S12 400m Freestyle silver with a British record in the first of five events on her Paralympic debut.
The prodigious 16-year old from Chertsey finished fourth in this event at last year’s European Championships but underlined her potential by breaking the short course world record earlier in 2012.
Having already sliced 3.5 seconds from her British record to qualify fastest from the heats, Russell knocked another three off in the final as she touched in 4:38.60 behind Russia’s champion Oxana Savchenko (4:37.89).
And despite missing out on gold by less than a second in a nail-biting dash for the wall, Russell insisted her expectations coming in to the meeting had been modest.
“It’s a dream come true,” said Russell. “I’ve come here to try my best so to come away with a medal is a bonus and a cherry on top. I can’t believe it."