Grabsch was not one of the fancied riders before the race
Germany's Bert Grabsch demolished the opposition to claim the men's time trial title at the road cycling world championships in Varese.
With Olympic gold medallist Fabian Cancellara absent, it was one of the most open time trials for years and Grabsch seized the chance.
Canada's Svein Tuft took the silver medal with US rider David Zabriskie in the bronze medal position.
Britain's David Millar came ninth and team-mate Steve Cummings was 25th.
Grabsch, who finished fourth at last year's world championships, clocked a time of 52 minutes 1.60 seconds to finish comfortably clear of the rest of the field.
Cancellara was the red-hot favourite to retain the title he claimed last year, but the Swiss cited fatigue as the reason for his withdrawal.
It opened the door for someone to come through, and Grabsch produced a fabulous display of sustained pace to claim the lead with 12 riders still to finish.
But the likes of Millar, Gustav Larsson and Levi Leipheimer could not get close to Grabsch's time over the 43.7km course.
Leipheimer, one of the pre-race favourites, was never really in the mix as he had to settle for fourth place.
"I am overjoyed. This is my biggest achievement and a nice birthday present for my wife Susanne," said Grabsch.
"Cancellara's not here, but I said well before the race that at least 10 guys could win this title.
"It was a perfect course for me. It was rolling, fast and it didn't have any real climbs. I couldn't have asked for any better."
I'm not feeling my age - I'm feeling the length of the season
Millar admitted he had fallen short of his own expectations after finishing well outside the medals.
"It started off good, but then I didn't have it in the second half. It was just average, which is very disappointing, because I was expecting a lot more," said the 31-year-old.
"It was not a good day at the office.
"I can't explain it. I thought I'd done everything right. I've done a lot of work these last five weeks. I expected a lot more.
"I'm not feeling my age - I'm feeling the length of the season."
1. Bert Grabsch, Germany, 52 minutes, 1.60 seconds.
2. Svein Tuft, Canada, 52:44.39.
3. David Zabriskie, United States, 52:53.87.
4. Levi Leipheimer, United States, 53:07.02.
5. Gustav Larsson, Sweden, 53:07.44.
6. Stijn Devolder, Belgium, 53:17.01.
7. Tony Martin, Germany, 53:17.86.
8. Janez Brajkovic, Slovenia, 53:26.76.
9. David Millar, Britain, 53:26.86.
10. Sylvain Chavanel, France, 53:27.42.