Down but never out, Katherine Grainger took a deep breath two months ago and resolved not to let the despair sink her spirits. In rowing, you expect to be buffeted by the tides, to feel the winds pushing you back when every corner of the lungs is aching to accelerate speedily forwards. But not this.

The reigning Olympic champion was set for a dethronement in absentia as British Rowing prevaricated on whether she and her partner Vicky Thornley were worthy of a ticket to Rio, on whether their gamble to invite the Scot back into the fold following her post-2012 sabbatical was destined to backfire when even a medal at May’s European Championships proved elusive.

They rolled the dice. Grainger, as she has done so often during a career sans pareil, bet on herself. And the British pair hit the jackpot yesterday with a performance beyond all expectations to take a double sculls silver that came so close to being a glorious gold.

With the blazing sun glistening off the statue of Christ the Redeemer that overlooks this lake, a miracle beckoned as they surged into a lead that held firm with 500 metres to go. Yet Poland’s Magdalena Fularczyk and Natalia Madaj likewise saved their best to last. And in a desperate lung-inflaming burst for the line, they dramatically snatched gold by 0.49 seconds that seemed barely visible to the naked eye.

Grainger fell back into Thornley’s arms and smiled euphorically. This is what made every shred of anguish worthwhile. “I’ve been to the Olympics before, I know how special it is and how worthwhile it is, I am bit of an eternal optimist and I felt that it would work out if we could find our way through those low times,” she said. “In a way it makes all the results more sweet if you’ve been through the mill and come out.”

To become, at the advanced age of 40, the UK’s greatest-ever female Olympian of the modern era, with one gold and four silvers, corralled through stops in Sydney, Athens, Beijing, London and now here. “It’s unreal,” she acknowledged. “It’s not something you set off to do. I started off as a student and at my first Olympic Games, it was just incredibly to be selected for and to get a medal back in Sydney, which is now 16 years ago.

“I continued it because I love this sport and I love being in a boat with people like Vicky and the passion and the excitement, the pressure of these big Olympic moments. That’s what drives me every single day. By following that dream, it’s got me to this place but I never set out to do it.”

This, said Sir Steve Redgrave, was “her best-ever medal”. Done with immense help from Thornley, who capsized when she first tried her hand at rowing seven years ago as part of a talent search programme but whose capacity for improvement must surely remind the Scot a little of herself.

The 28-year-old’s natural talent is still in its prime. Grainger, fifth time around, has needed more coaxing then ever before. “I was pushing her on a little bit to start a bit because I said it would take her as long to get back as she had been away,” her coach Paul Thompson revealed.

“She was out for two years and she’s just come back in time. Better late than never. That doesn’t take away from Vicky. Since London when she finished fifth in the eight, she’s just completely thrown herself at it and been so single focused. It’s a really just reward for them both.”

There have been creative tensions at times, Grainger hinted. Inevitable over 15 years that have also brought six world titles. But there is a deep mutual respect from which both have profited. “Sport is a very tough, intense environment to work in. We’ve all said and done things you know that have particularly been tough along the way, but it proves what a great working relationship we have to come out with a result like that.”

Thornley has time left for more accomplishments. Grainger is taking her leave. When she opted to return in 2014, it was her mother to whom she was most nervous about breaking the news. Her parents feared she might disappoint herself, that mortality would bring pain over joy. These Games, she vowed, are her last. The incredible journey ends here. For their sake, as much as hers.

“I’ve got a lot of friends and family who have been a lot of support along the way, my mum and dad in particular,” Grainger said. “They’ve been through it five times with me. They weren’t sure if coming back was the right thing for me and they've been so supportive since I did. We all know it was the right decision now. But at the same time, I think maybe that’s enough.”

Onto the next thing, a new chapter, fresh challenges. Maybe to use her specialist legal knowledge of murder and make a killing. Perhaps into academia. Surely she will become a Dame with a roving remit to inspire. What next, we wondered?

Another broad smile. But no definitive plan. “It’s been minutes since my Olympic career has finished - I haven’t quite mapped out that,” she laughed. “I tell you what - for the first time in a long time I don’t set the alarm tomorrow morning and I wake up whenever I want and it will be a new dawn for a new start. I don’t know what it will be.” Onwards, she goes. And surely upward ho.