Patience, the London 2012 silver medallist, and Grube recovered from a challenging first race, in which they finished 21st, to sail to 5th place in race two and end the day 11th overall.
The Brits have each spent between 90-150 days in Rio during this Olympic cycle preparing for what was always going to be a testing, unpredictable event.
But Patience admits to never having been confronted with the conditions they experienced inside Guanabara Bay today, and now the pair can't wait to start building on what they learned.
Patience said: "We've been training out here collectively as a team for three years and I would honestly say I've not seen those conditions yet.
"The wind was really coming from far round to the west it was. It really was coming out over the city and the hills and normally the high land funnels it, but it didn't seem to do that today.
"It was impossibly hard to predict what was next, you really had to go with what you saw and there was a bit of hoping what you've seen is going to establish and carry you through to where you need to be. All you can do is sail in the wind around you.
It was heart in mouth for a lot of moments, for everyone."
Rio marks Grube's Olympic debut after the man affectionately known as Twiggy resurrected his former partnership with Patience in December after Patience's crew Elliot Willis was diagnosed with cancer in late 2015. Today marks the culmination of eight months of hard work to get to the start line and they couldn't be happier.
Twiggy added: "My first day at an Olympics is awesome, it's been a long time coming. We're in a good position, working hard and now is the time when all that hard work means you're able to relax and race as hard as you can. Luke's experience is helping us through, especially on days like today when it would be easy to panic."
Luke added: "It feels as though we've pulled this whole beast together just in time for day one and we're absolutely fine. I'm proud of what we did today, proud of how we've managed to come out after the short time available we've had available to do this. So it's all smiles and we're ready for tomorrow."
Double World Champions, Sime Fantela and Igor Marenic (CRO) have taken an early lead with Australia's three-time World Champions, Mat Belcher and Will Ryan second and Daniel Willcox and Paul Snow-Hansen (NZL), silver medallists at this year's Worlds, in third.
The 470 Men's class is scheduled to contest an 11 race series, with two races per day on 10, 11, 12, 14 and 15 August before the final one off medal race on Wednesday 17 August.
To follow Luke and Twiggys fortunes at Rio 2016 visit www.rya.org.uk/Rio2016, follow @BritishSailing on Twitter and like us on Facebook at www.facebook.com/britishsailingteam