Mezger (31) said before he left he expected some form of torture in the arduous race over lava rocks in hot conditions, an event in which he first competed last year, finishing 11th male in his age-group in just over 3hr 18min.
But he found the best-laid plans to break into the top 10 can turn to dust when equipment fails.
Mezger said in an email this week he had a great preparation for the race "and all was going perfectly".
He was delighted with his 1500m swim (21min 39sec), exiting the water ahead of three of his main age-group rivals.
His transition to the 40km bike went well and he was holding his place until a rider crashed in front of him and Mezger went over the top, puncturing a tyre.
It took 5min to fix the flat, while dodging other competitors, but once he was back on his bike he broke his rear derailleur at the 6km mark.
"After realising that it wasn't fixable I tried to turn the gears into a single speed. That only got me about 20m and then the chain was off. So, I had two options, turn around and do not finish or run the rest.
"So the sensible quick decision was to finish the race and run the bike for the next 25km. So I picked up the trash, helped riders with tools and fixed two flats for people.
"On the downhills I was able to coast until I got another flat. Since I'd used my only tube I had to run and was lucky enough to find a spare new tube on the ground."
After a long run in bike shoes, Mezger made it to transition for the 10km run with a couple of new blisters.
He passed 80 runners to finish in 347th place (4hr 20min 59sec) of 482 athletes who finished. There were 550 entrants.
"I'm disappointed with the results but of course more than happy with the effort and the experiences over the past 12 months leading up to it," Mezger said.
The first professional athletes to finish were Ruben Ruzafa, of Spain (2hr 37min 36sec), and Julie Dibens, of Britain (3hr 3min 57sec).
The amateur champions were Francois Carloni, of France (2hr 54min 26sec), and Keri Grose, of Australia (3hr 34min 4sec).
