The 27-year-old headed to Eton Dorney with lightweight double sculls partner Mark Hunter as the boat to beat having claimed the Olympic title four years earlier in Beijing, as well as topping the podium at the 2010 and 2011 World Championships.
But it wasn't to be as the British duo failed to defend their Olympic crown, seeing it pass on to Denmark's Mads Rasmussen and Rasmus Quist Hansen with Purchase and Hunter having to settle for silver.
In the aftermath the two scullers apologised for being 'failures' and Purchase admits the memories of that day are still fresh in his mind.
"It took me a long time to develop the courage to watch it back," said Purchase, who is taking a year away from the sport before deciding on whether to continue to the Rio 2016 Games.
"I have watched it twice and each time I never really realised just how close it was at the finish and it is hard work to watch it. It won't ever be something I will enjoy watching, but I need to be able to watch it to come to terms with it and move on.
"As Olympians you go there to try and win and there is no point in going there to come second. It doesn't matter if it was a home crowd or not, but for me it was the one Games I wanted to target and to go there and perform well.
"In hindsight, we did a fantastic race, we put together one of the best races of our career together, Mark and I, so I have got to be happy about that, but I will always be slightly upset about the result and always have that slight 'I wish I had' [feeling]."
- Sports & Recreation
- Rasmus Quist Hansen