The Yorkshire duo became the first British siblings in Olympic history to finish first and second in the same event and the maiden brotherly one-two since Italian equestrians Piero and Raimondo D’Inzeo in 1960.
They were neck and neck, having broken away after two kilometres of the 10km run, until Alistair, the eldest by two years, made his victory dash, only slowing to collect a Union Jack and the Yorkshire Rose. He finished six seconds clear of Jonny in 1:45:01.
“It’s very special to retain the title,” said Alistair, 28. “I’ve trained as hard as I can this year and executed it on the day. The record isn’t the big thing for me, it’s about turning up on the day and winning the race.
“Maybe the enormity of it all will sink in over the next few weeks but I’m just pleased I turned up and Jonny did it as well.
“The odds are it won’t happen again. Four years is a long time to Tokyo but I don’t think we should be thinking about that at the moment. I think we should just enjoy what we’ve pulled off today.”
Jonny, who upgraded his London 2012 bronze, added: “In training I’ve maybe been a little bit better than Alistair but maybe the short stuff suits me a bit more.
“I might have done a bit too much work on the bike but when we got to the run Alistair was too strong for me and these hard races suit him a bit better than me.”
Sailors Hannah Mills and Saskia Clark, meanwhile, safely navigated their rescheduled final race to claim gold in the women’s 470, in turn overcoming the New Zealand team which had beaten them at London 2012.
The pair were forced to wait 24 hours to commence celebrations after a lack of wind in Marina da Gloria throughout Wednesday. They finished eighth of 10 finishers to beat New Zealand’s Jo Aleh and Olivia Powrie by 10 points overall.
“I can’t believe it,” said Mills. “It has actually been the best feeling ever.
“We have forgotten all about London. We are so proud to come back after it and we’ve worked so hard to get the upgrade to gold.”
Great Britain’s success did not stop there. Liam Heath and Jon Schofield claimed silver in the men’s 200m kayak double, surging over the line to beat their Lithuanian rivals by 0.014 seconds. Marcus Ellis and Chris Langridge also hit the podium, winning bronze to net Team GB’s first Olympic badminton men’s doubles medal.