Great Britain pair Hannah Mills and Saskia Clark will secure a gold medal in the 470 sailing event as long as the helmswomen finish the medal race on Wednesday.
The remaining nine teams will now battle it out for the silver and bronze medals on offer with Mills and Clark taking a 20-point lead into the final race.
New Zealand duo Jo Aleh and Polly Powrie had challenged the Brits but two disqualifications – one for a U-flag false start and the other for unsporting failure to take a penalty turn – was enough to put first place out of reach for them.
The other contenders for the last two medal positions are Tina Mrak and Veronika Macarol of Slovenia, France's Camille Lecointre and Helene Defrance, Japan's Ai Kondo Yoshida and Miho Yoshioka and Annie Haeger and Briana Provancha of the United States.
"It feel like we've been sailing forever to get this gold," Clark told the BBC. "It's completely surreal. We've sailed out of our skin in a marathon event."