The 37-year-old secured two bullets - sailing terminology for victory - yesterday and picked up where she left off, with another race win today and then a fourth.
Lucas, the only woman in the fleet, has an 11-point cushion over second-place German Heiko Kroger and looks on course for Britain's first medal since Sailing joined the Paralympic programme in 2000.
'It was a really long day,' she said. 'We must have been on the water for about six hours with really shifty conditions. It was a great first race and then I had to work hard in the second race.'
She added: 'Heiko won the second race, which is fine as I've still managed to take a couple more points off him today, which is brilliant.
'Whatever it brings tomorrow I'm looking forward to it and if I can have another good day on the water it would be fantastic.'
In the Two-Person Keelboat (SKUD18) there was an initial delay to racing and the fleet twice had their first race of the day abandoned.
Australia's Dan Fitzgibbon and Liesl Tesch made the best of the capricious winds to finish second in the first race and win the second after leading from the start.
They sit in first place in the overall table, with a four-point lead over USA pair Jen French and JP Creignou, who are tied on points with third-placed, Alexandra Rickham and Nikki Birrell of Great Britain.
Variable conditions in Portland Harbour meant the Three-Person Keelboat (Sonar) racers only got one race today.
Holland's Udo Hessels, Marcel van de Veen and Mischa Rossen continue to dominated proceedings - they won the race and have an 11-point cushion over the second-placed German crew in the overall standings.