Dennis was racing for the first time since his sudden withdrawal during Stage 12 of the Tour de France in July.
Few expected the reigning champion to defend his title, but Dennis averaged 49.7 km/h over the 54 km course to win by more than 1 minute over his closest rival.
“It’s been a long route to get here since July,” Dennis told a news conference. “There are a lot of people to thank. It’s not just been tough for me, it’s been tough for them too. It’s really special to back up this year and come here in the best possible shape to defend this title and show that I haven’t hung up the bike.
Dennis is Australia’s second multiple time trial world champion. Mick Rogers was a three-time winner from 2003-2005.