Patience and Bithell are just four points behind the Australians Mathew Belcher and Malcolm Page who scored two race wins, with the British pair taking a second and third.
Both boats have an unassailable lead over the Argentinians and Italians and will fight it out for gold, with Patience and Bithell needing to beat the Aussies with at least one nation between them.
“It is a two-horse race now, we can finally say that,” Bithell said. “To have secured at least a silver medal feels fantastic but it hasn’t sunk in properly yet.
“We’ll celebrate the small success of that then have a day off tomorrow then we get cracking on the medal race day to see if we can go one colour shinier.”
Hannah Mills and Saskia Clark still have gold in their sights as they head into the final three races of the women’s 470 in second place, four points behind New Zealand’s Jo Aleh and Olivia Powrie and three ahead of Dutch pair Lisa Westerhof and Lobke Berkhout.
“We are definitely happy with where we are at the moment,” Clark said. “To be up there fighting for the top spot, we would have definitely taken that at the start of the week.
“We just want to make sure tomorrow we have another consistent day so that we are still fighting come the medal race.
“We’ll be happy to go into the medal race with a chance of winning – the Nothe course has shown if you are in that position you are alright, anything can happen.”
Bryony Shaw was unable to repeat her bronze medal success from Beijing in the women's RS:X class as she finished the medal race in fifth, having started the day with the possibility of a bronze.
And the Elliott 6m women’s match racing team of Lucy Macgregor, her sister Kate and Annie Lush started their quarter final match best of five against Russia with one win and one loss.