Swimming ten kilometres in 1hr 51min 51.6sec is strictly for men who snack on leg of ox, take on the Channel as though it were a length of the local baths and pass the odd steamship on the way to climbing out by scaling the White Cliffs. But for one iron man among the 25 who raced in the first Olympic marathon swim in Shunyi Lake yesterday, that challenge was no match for the enemy within that he fought and defeated.

At 19, Maarten van der Weijden, of Holland, had acute lymphatic leukaemia diagnosed. Given only a slim chance of survival, his treatment included chemotherapy and a stem cell transplant, the scars of brain surgery still visible on his shaven head. At 27 and three years beyond need of medication, he is the first Olympic ten-kilometre marathon champion, a man hailed as swimming's Lance Armstrong. As others limped away from the pontoon after a blistering final in which the courage of David Davies delivered a silver medal for Great Britain, the experienced Dutchman had a spring in his giant step.

At 6ft 7in, Van der Weijden is truly a monster of the waves. Where 23-year-old Davies, whose medal was all the more remarkable for the race being only his third over the distance, described the champion as being “like a man mountain”, Mark Warkentin, the American who finished eighth, said: “Maarten's like this huge liner that you can't get round, and we're like little yachts being washed away.”

The Dutchman relied less on physical size, however, than his mental capacity to deal with pain, pay attention to detail and draw on experience. “The pain and fatigue that you feel in the water is what I went through for a whole year to beat the cancer, so I know what to expect,” Van der Weijden said.

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Given a new lease of life, Van der Weijden leaves nothing to chance. He has spent his nights in Beijing sleeping in a low-oxygen tent in his room at the Olympic Village to simulate high-altitude conditions and worn glasses fitted with lights that wake him up fast and help him to produce naturally what the Holland team doctor described as “higher levels of cortisone” and conquer pain.

Van der Weijden dedicated his gold medal to all who had donated money for cancer research. “I am thrilled. Without their generous donations I might not be here,” he said.

One battle had helped him to prepare for another. “The leukaemia has taught me to think step by step,” he said. “When you are in hospital and feeling so much pain and feeling so tired, you don't want to think about the next day or week - you just think about the next hour. It teaches you to be patient when you are lying in a hospital bed and that was almost the same strategy I chose here, to wait for my chance in the pack.”

Davies led that pack for nine kilometres, trying to stay clear of the scrum but helping his rivals at the same time. English Institute of Sport experts estimated that Davies had used up to 15 per cent more energy by leading the way. With 400 metres to go, his “head spinning and body gone”, a disorientated Davies headed for the far buoy of the home-straight finish lane instead of the near side, taking Thomas Lurz, of Germany, with him. Van der Weijden seized the day, tucked in to the finish lane with a two-metre advantage as his rivals headed across the course and maintained the lead over the final 100-metre sprint.

The gold was his, 1.5sec ahead of Davies, with Lurz 0.5sec further adrift. The battling Briton said: “His story is amazing and can inspire a lot of people. What he has achieved is phenomenal.” The same could be said of Davies.

Only eight months ago, he and Kevin Renshaw, his coach, sent a stern “no” to a request from Sean Kelly, the Britain head open-water coach, to join the hunt for marathon medals. Kelly sat up until 2am on the eve of Christmas, composed an e-mail outlining “all the positives”. He hit “send” and said his prayers. The answer came later that day: “We'll do it.”

Davies intends to do it again at London 2012. “I'd really like to swim in the Serpentine, it'll be a fantastic spectacle,” he said. “I hope to go one better in front of a home crowd.”