"It was really good with the first half of the race because of the rain, but it was a bit harder in the second half as it was getting quite hot," he said.
"The plan was to have a nice run for the first 60km and I think I managed to have a good race for the first 60km, then I tried to keep a good pace after that."
David Byrne from Australia finished second about 20 minutes back from Buud, during his first race longer than 60km, and South African Ryan Sandes finished third.
Buud came close to beating the race record, which was set last year by Dylan Bowman (US) in 7h 44m.
Hayvice was rapt to win the women's title today and finished about 20 minutes ahead of Melissa Robertson (Australia). Fiona Eagles finished third.
Muir said she started well, to try and defend her title, but suffered with a bad stomach.
"I went out pretty well ... but we had to pull the pin because of a crook stomach," she said. "I tried to get some food down [during the race] but it kept coming up."
About 1300 competitors took part today in the 60km, 85km and 100km distances.