The British pair will start eight points clear of Brazilians Robert Scheidt and Bruno Prada after being the dominant force all week.
Percy and Simpson won race ten after a fourth in race nine and will have their fate in their own hands when they bid to become the first British sailors to take glory in Weymouth.
Apart from coming 11th in the opening race of the regatta, the British pair have been in the top three in eight of the other nine races – with three wins.
Victory at the weekend will take Percy to a momentous third Olympic gold medal and he cannot wait to get back in the water.
“It’s going to be an incredible spectacle win, lose or draw,” said Percy. “There’s three boats in it now – three teams of sailors who’ve just been in unbelievable form.
“It has been incredibly frustrating as me and Andrew have probably sailed the best we ever have and we can’t get any distance on them.
“And it’s so unusual for the Star class to have three boats dominating against multiple medallists.
“What’s been amazing this week, the three leading boats have sailed with so much respect for one another – and it has been a real pleasure to race those guys on real form.”
The 470 pair of Luke Patience and Stuart Bithell continued their explosive start with a fourth and a second to pull six points clear of Australian world champions Matthew Belcher and Malcom Page.
In their first Olympics the duo are not letting themselves get overawed by the pressure of performing in front of their home crowd.
“We’re not intimidated at all,” said Patience. “We’re enjoying it, loving it – we revel in the challenge and I hope we can continue to tick the right boxes off and do what we need to do to allow the races to take care of themselves.
“It’s the Olympics but we treated it like a regatta from the start – it’s still the same guys we raced round the world tour with and it’s just a different title on the sailing instructions when you read them at the start.
“Obviously it means a lot more and this is what we work towards but it’s just sail boat racing.”
Their female counterparts Hannah Mills and Saskia Clark finally got their quest for gold underway after watching from the sidelines for most of the first week.
And the pair took a win in race two to follow a sixth in their opener, a result which could have been much worse after an edgy start that saw them given a penalty turn on the start line.
“There were definitely some nerves this morning,” Mills confirmed. “We’ve been waiting quite a while to get going and the whole fleet was just so excited to finally get out on the water and get racing.
“It probably did affect the start of the first race as our goal for the day was to not do anything stupid and immediately we went and crashed into the pin end so we definitely did something stupid.
“But it almost helped us in a way as we did our penalty turn and got on with our race knowing we couldn’t afford to be nervous after that – we had to make a good comeback and we did that really well so we’re happy.”
The result leaves the 470 team leading overall but Clark was quick to confirm they were not getting ahead of themselves in their first Olympics as a duo.
“Winning our first Olympic race was an awesome feeling as I didn’t win one in Beijing and winning one at the Games is a pretty big deal but in context we’ve got a lot of races to go,” Clark said.
Paul Goodison’s dreams of retaining his title from 2008 are in tatters as he endured another bad day as he battles his back injury.
He was never able to get going and a 17th and a 12th leave the Laser sailor in eight place, 31 points off bronze medal position.
Stevie Morrison and Ben Rhodes enjoyed two firsts yesterday but were unable to repeat their heroics in the 49er class and a mixed day saw them finish 17th, fourth and 20th but they remain in contention for a medal in fourth overall.
Alison Young is fifth overall in the Laser Radial after a solid but unspectacular day saw her finish sixth and eighth, but with two races left before the medal race she is in the fight for a podium finish.