German pair Rico Freimuth and Kai Kazmirek took silver and bronze while twice former world champion Trey Hardee was one of more than a dozen of the original 35 starters who dropped out over the course of the notoriously tough contest.
Olympic silver medallist Mayer led from the shot put on Friday morning and looked to be cruising to his first world gold until he decided to skip the opening pole vault heights and enter the fray at 5.10.
The move nearly proved disastrous as he missed his first two attempts, then grazed the bar on his third.
Despite an unnerving wobble, the bar stayed in place and Mayer avoided a zero score which would have wrecked his chances, instead increasing his lead over Rico
He comfortably came through the javelin and 1,500 metres, the final of the 10 events staged over two exhausting days, to see himself safely home.
Mayer finished on 8,768 points with Freimuth, with 8,564 and Kai Kazmirek 8,488, taking the silver and bronze medals.
"I am so, so tired. I cannot even imagine I am the world champion," said Mayer. "The first day was perfect. I am so proud. This competition was so hard. I just wanted to finish it ... I was so anxious."
Hardee, fifth overnight, pulled out after a miserable morning in which he failed to pick up any points in the first two events.
He clattered into the third hurdle in the 110 metres hurdles, then produced three foul throws in the discus before calling it a day.
The event was left open by the retirement earlier this year of American Ashton Eaton, who had dominated recently, winning the last two Olympic and world titles.
Canadian Damian Warner, often seen as the man most likely to break Eaton's dominance, finished fifth.
(Editing by Ed Osmond, Neville Dalton)
Share
