Long first competed at the 2004 Games in Athens aged just 12 and won three gold medals before securing a further four titles, a silver and a bronze four years later.
Coming into London, the 20-year-old set a new world record in the 100m Butterfly - S8 and yesterday she successfully defended her title at the Aquatics Centre.
Yesterday I could celebrate my gold medal and today I put that behind me. It's a very long race and my mind wanders and I think of other things and then I think, slow down, it's only a morning race, but it felt really good.Jessica Long
Long returned this morning to qualify fastest in the 400m Freestyle - which she won in both 2004 and 2008 - in a new Paralympic record of 4:44.52, almost 14 seconds ahead of second-placed Heather Frederiksen of Great Britain.
The time was just 0.35 outside her own world record and puts her in an excellent position for tonight's final.
Long said: 'Yesterday I could celebrate my gold medal and today I put that behind me. It's a very long race and my mind wanders and I think of other things and then I think, slow down, it's only a morning race, but it felt really good.'
In the men's equivalent there is the possibility of a British clean sweep.
The Hynd brothers, Sam and Oliver, and Thomas Young filled the first three slots in qualification to raise the spectre of a repeat of their one-two-three at last year's European Championships in Berlin.
The elder Hynd - the defending champion and world record holder - felt his race had gone to plan and he said: 'A very good swim, I was really pleased with how it went.
'The tactics were right on what me and my coach set. I'm glad to get the heat out of the way. All the pressure's off after that.'
As well as Long, there were Paralympic records for Andre Brasil in the 50m freestyle - S10 (23.50), Ashley Mortimer in the women's equivalent (28.21) and Timothy Antalfy in the 100m Butterfly - S13 (56.03).
Bradley Snyder's effort of 57.18 in the 100m Freestyle - S11 was 0.51 outside John Morgan's world record which has stood since 1986.