Ferry Weertman won the gold medal in the men's 10 kilometres open water swimming, just 24 hours after Dutch compatriot Sharon van Rouwendaal's victory in the women's race along the same course in Rio.
It is the first time one National Olympic Committee has won both women's and men's events in marathon swimming at the same Olympic Games.
Unlike van Rouwendaal, who had won by a huge margin, Weertman only managed to secure victory after a dramatic battle to the finish with 10 of his rivals, stretching up to touch the finishing board just fractionally ahead of Greece's Spiros Gianniotis.
The Greek won his first medal in this this event after competing in all three Games it has been held - 2008, 2012 and 2016.
Gianniotis led the way into the finishing funnel and, even though he might have crossed the finishing board first, he missed the finishing wall with his hand which gave Weertman time to touch it first.
"It means a lot, I've been working very hard for six years to get to the Olympics," said Weertman.
"It was such a tough race from the start.
"I did my little share at the front which I don't normally do that early in the race.
"It made it a little bit tougher for me."
"Even after I touched the wall, I wasn't sure I'd won.
It took me a while.
"I called my friends back home and they said 'you won, you won' and I'm like, 'Oh really?' I couldn't believe it. I still can't believe it."
France's Mac-Antoine Olivier was awarded bronze ahead of China's Zu Lijun.
Meanwhile, defending Olympic champion Ousamma Mellouli of Tunisia came 12th.
There was more controversy in the marathon swimming though, a day after an incident in the women's competition meant the runner up was disqualified.
Great Britain’s Jack Burnell described the refereeing as “an absolute joke” after he was disqualified at the end of the race for making unnecessary contact with other swimmers.
“They’re giving yellow cards out left, right and centre for absolutely nothing, and then disqualifying people two metres from the end when there’s people grabbing hold of legs and everything," he told the BBC.
"The whole thing was ridiculous, an absolute joke.
“In the end apparently I was disqualified, about two metres from finish.
"The first yellow card I got was coming down the straight back here - I was second, there was nobody either side of me, and the guy pulls out a yellow card.
"I couldn’t have physically touched anybody."